Suppression of the protests sparked worldwide anger
A 75-year old Chinese academic is in hospital after receiving what he called a brutal beating at a cemetery.
Sun Wenguang said he had been trying to pay his respects to the late communist leader Zhao Ziyang, who was purged for supporting the 1989 Tiananmen protests.
Mr Sun, 75, had visited Mr Zhao's grave annually, but this year marks the 20th anniversary of the Tiananmen crackdown.
The Chinese government treats its crushing of pro-democracy protests on Tiananmen Square as taboo.
"I still can't move now. I'm just lying in bed. What they did was audacious and unprincipled. Very savage. Especially as they did it to me before thousands of people," Mr Sun said from a hospital in Shandong's Jinan city.
"They wanted to punish me and let people know that Zhao Ziyang is not allowed to be memorialised," he claimed.
He said he had suffered three broken ribs and injuries to his hands and legs in the attack at the Revolutionary Martyrs Cemetery in Jinan on Saturday.
"Five minutes after I went in, five strong men suddenly appeared. They punched and kicked me until I fell to the ground and could not move any more. I'm 75 years old, you know," he said.
He said he had paid his respects at the grave every year, to mark the Qingming grave-sweeping festival, but was warned not to do so this year by police and officials at Shandong University, where he used to teach.
Mr Sun is a retired physics professor and has spent more than a decade in prison at various times from the 1960s to the 1980s, for criticising communist revolutionary leader Mao Zedong.
The attack on Mr Sun comes two months ahead of the the 20th anniversary of the Chinese military's crushing of the 1989 Tiananmen Square pro-democracy protests, which led to the purging of Mr Zhao.
He had opposed the use of force against the protesters, hundreds and possibly thousands of whom subsequently died in the crackdown.
Mr Zhao died in 2005 under house arrest, and was denied the sort of funeral generally accorded former leaders.
The New York-based group Human Rights in China issued a statement condemning the attack on Mr Sun.
"This deplorable act, committed in broad daylight and in clear view of the police... calls into serious question officials' professed commitment to building a society that puts people first," said executive director Sharon Hom.
In other ceremonies performed for Qingming, police in Beijing took away several people on Sunday who were commemorating the death of Yang Jia, who was executed last year for killing six policemen in a stabbing spree in Shanghai.
Mr Yang became widely popular after reports that he had been tortured by police while being questioned about an unlicensed bicycle.