Blind activist Chen Guangcheng's nephew was jailed for three years and three months by a Shandong court yesterday, Chen said.
He condemned the sentence as retaliation for his daring escape from house arrest earlier this year.
Chen Kegui , 32, was convicted in Yinan County People's Court of "intentional injury" for assaulting officials who stormed into his house in April to look for his uncle who had escaped from his tightly guarded home in Dongshigu village, said Chen Guangcheng , who now lives in New York.
Chen fled to the US embassy in Beijing just before US Secretary of State Hillary Rodham Clinton visited China, setting off a diplomatic tussle.
Court officials confirmed Chen Kegui's trial took place but could not be reached to confirm the sentence.
Chen Kegui was earlier charged with "intentional homicide", but no one died and the charge was later changed to "intentional injury".
Chen Guangcheng's wife, Yuan Weijing , said yesterday that Chen Kegui was defending himself when he attacked officials with knives as "he would have been beaten to death otherwise". Officials had also tied Yuan to a chair and threatened her after her husband escaped, she said earlier.
Chen Guangcheng said the sentence was "a blatant declaration of war to humanity, equality and justice".
"This is telling the world that there is no need to have any hope in the new government," he said, referring to the Communist Party's leadership transition last month. He accused the authorities of failing to investigate the abuses he and his family suffered for years, as was promised in an agreement with the United States after he sought refuge at the US embassy.
Chen Kegui's father, Chen Guangfu, said he and his wife were barred from entering the court house yesterday by dozens of plain-clothes police. He said he never received an indictment detailing the charges against his son and was only told about the trial by court-appointed lawyers four hours before it started. Family members had not been allowed to hire their own lawyers.
Hated by local officials for exposing forced abortions and sterilisations in Shandong, Chen Guangcheng was jailed for more than four years in 2006 on what his supporters say were trumped-up charges. After his release in 2010, he and his family were confined to their home.
Professor Jerome Cohen, a US-based expert on mainland law, said the fact that Chen Kegui's parents, witnesses to the assault, were barred from testifying was "an ultimate example of judicial farce in China".
"Not a happy example of how human rights will be protected by China's new leadership," he said by e-mail.
Additional reporting by Laura Zhou, Teddy Ng