A Chinese court has thrown out a guilty verdict against Chen Guangcheng, an activist who raised concerns about forced abortions.
Rights groups insist Chen, who is blind, did not get a fair trial
"It was found that there have been serious violations in the legal procedures," said Mr Chen's lawyer.
Mr Chen, 34, was found guilty of public order offences in August, and sentenced to more than four years in jail.
His case drew international criticism, with rights advocates saying he did not receive a fair trial.
The Linyi City Intermediate Court has now quashed Mr Chen's conviction, and ordered a retrial.
The BBC's Beijing correspondent says successful appeals are extremely rare in China's court system, so the ruling on Mr Chen came as a welcome surprise to his lawyers and family.
His case will go back to a lower court in Yinan County, one of Mr Chen's lawyers, Li Jingsong, told the BBC.
"The court said it was because the process of the first trial was unfair and facts and evidence... were not tenable and did not hold water," Mr Li said.
"This case is also a victory for justice in the world, as being a defence lawyer I have seen that it has received international support," he added.
The retrial should take place within two months.
Chen Guangcheng was sentenced to four years and three months in jail for "damaging property and organising a mob to disturb traffic".
The official Xinhua news agency reported that he had launched an attack on government offices and police cars in Yinan County, because he was upset with workers carrying out poverty-relief programmes.
But Mr Chen's supporters said that local officials had fabricated these charges, in order to punish him for exposing violations of China's one-child policy.
Mr Chen had accused local health workers in Linyi city, in Shandong province, of forcing hundreds of people to have late-term abortions or sterilisations.
His allegations were covered in the international media, including an article in Time Magazine which claimed some 7,000 people had been sterilised against their will in the province.
Several workers were later arrested or sacked over the claims, state media reported, acknowledging "successive complaints" about illegal practices in Linyi.
China brought in its one-child policy 25 years ago, in a drive to curb population growth. But forced sterilisation and abortion are illegal.