A Chinese-born American scientist who conducted U.S.-funded research on detecting North Korean nuclear explosions has spent nearly two years behind bars in China, where he now faces espionage charges — a situation his wife and advocacy groups say amounts to wrongful detention.
The case involves Youlin Chen, a 54-year-old Boston resident who became a U.S. citizen in 2011. His situation, being reported publicly for the first time, adds another layer of friction to an already strained relationship between the two nuclear powers, even as President Donald Trump works to keep diplomatic ties stable in the wake of last year’s trade war.
Secretary of State Marco Rubio officially designated Chen as “wrongfully detained” on March 19, making securing his freedom a top U.S. priority. According to his wife, Yufang Rong, the Trump administration has chosen not to announce this publicly in order to leave room for behind-the-scenes diplomacy.
A U.S. source with knowledge of the case, speaking anonymously to discuss sensitive diplomatic matters, said the administration remains “focused on gaining his release from his unjustifiable detention.”
Rong said she has been informed by both the White House and State Department that during Trump’s state visit to Beijing in May, the president raised Chen’s detention directly with Chinese leader Xi Jinping, who pledged to look into it. However, Rong said Xi’s government has taken no action since then.
The U.S. source did not directly confirm that Trump brought up Chen’s case with Xi, but noted that the two leaders share a “very good personal relationship” and that “this is one of many facets in the U.S.-China relationship. No one issue is defining.”
Chen is currently the only American held in China who carries the wrongful detention designation, according to his wife and hostage advocacy organizations.
In an interview, Rong said she is deeply worried that Chinese authorities have already decided to find her husband guilty before his trial even begins. Espionage convictions in China can carry sentences ranging from lengthy prison terms up to life — or even the death penalty in cases considered especially serious.
“I believe they will convict him no matter what and the trial will be behind closed doors,” Rong said. She is also a seismologist but does not work on her husband’s research.
The Foley Foundation, a group that advocates for Americans held abroad and has been monitoring Chen’s case, estimates that at least 12 Americans are unjustly held in China, including those under exit bans. Elizabeth Richards, the group’s director of hostage advocacy, is among those tracking Chen’s situation.
Deputy White House press secretary Anna Kelly said: “President Trump has been clear that he wants every American detained abroad to return home, and he has reunited over 100 individuals with their families since taking office this term.”
The Office of the U.S. Special Presidential Envoy for Hostage Affairs and the Chinese embassy did not respond to requests for comment.
Questioned More Than 100 Times
Rong said U.S. embassy officials have visited Chen on multiple occasions, but Chinese authorities are always present during those visits, making it impossible for him to speak openly. A Chinese attorney she hired was not permitted to meet with Chen until more than 13 months into his detention.
According to Rong, Chinese officials have interrogated her husband more than 100 times, focusing specifically on his research into the seismic signatures produced by North Korean nuclear test blasts.
Eric Lebson, a former U.S. national security official whose hostage advocacy organization, Global Reach, is advising the Chen family, believes China is attempting to exploit Chen’s expertise to improve its ability to hide underground nuclear weapons tests. The technique in question, known as decoupling, involves detonating a device inside a large underground cavity to reduce the detectable shock waves it creates.
Lebson said nuclear testing experts consulted by his group expressed similar concerns.
The Trump administration accused China in February of using this very technique to conceal a low-yield underground nuclear test conducted on June 22, 2020. China, which has signed but not ratified the 1996 Comprehensive Nuclear-Test-Ban Treaty — as has the U.S. — denies carrying out that test.
Lebson noted that Chen works for a U.S. government contractor and has never held a security clearance or done classified work. His research into the seismic waves generated by North Korean nuclear tests was funded by the State Department and the Air Force Research Laboratory, conducted in partnership with Chinese academics, relied on publicly available Chinese data, and can be found online.
Reuters reviewed a December 2020 paper authored by Chen that analyzed the magnitude of North Korea’s six known nuclear test explosions and explored ways to tell their seismic signatures apart from those of earthquakes. The paper’s cover page states it was prepared for the State Department’s arms control bureau and was “approved for public release.”
Human rights organizations have pointed out that under China’s state-secrets law, authorities have sweeping power to retroactively classify previously public information — such as government statistics — as national security secrets, which could implicate anyone who used or shared that data.
Arrested at the Airport
Chen was taken into custody by Chinese state security agents on November 5, 2024, at Beijing International Airport just as he was preparing to board a flight back to Boston. He had been visiting family and delivering lectures about his research at two universities, according to Rong and Lebson.
Rong said that in the early weeks of his detention, Chen was subjected to “harsh conditions,” including being made to sit on a hard stool all day without being allowed to stand, read, or exercise. He was also unable to get medications he needs for diabetes and other health conditions.
Since those early days, Rong said it has become harder to get information about how he is being held. What she does know is that he has lost between 30 and 40 pounds (approximately 13.6 to 18.1 kilograms), receives inadequate food with little protein, fruit, or vegetables, and is given only low-quality medications.
Chen was formally charged with espionage on May 1, 2025, though his trial has not yet taken place. The case is expected to come up again when Xi visits Washington in September, a trip Trump has said is planned.
U.S. Senator Ed Markey, a Massachusetts Democrat who led two other senators in a December 17, 2025, letter urging Rubio to grant Chen the wrongful detention designation, said he is “deeply concerned about Dr. Chen’s safety and wellbeing.”
“It is my hope that increased attention on his unjust detention will force the Chinese government to do the right thing and release Dr. Chen,” Markey said in a statement.
