Human Rights Watch said comments last month by UNAIDS' chief Peter Piot that the Chinese government had adopted a more open attitude towards its growing AIDS problem were not merited.
"The Chinese government's intensifying crackdown on HIV/AIDS activists deserves international condemnation, not baseless praise," Joe Amon, the rights watchdog's HIV/AIDS director, said in a statement.
"UNAIDS should make it clear to the Chinese government that ongoing persecution of HIV/AIDS activists is wrong, counterproductive, and threatens efforts to contain the disease," Amon said.
Human Rights Watch said that activists in Guangdong and Henan provinces had been forced to abandon three meetings in recent weeks, in one case because the issue was considered "too sensitive" for public discussion.
"These individuals and groups dedicated to addressing the enormous suffering wrought by China's HIV/AIDS epidemic should not face police threats and harassment," Amon said.
"If the Chinese government had devoted as much energy to halting the epidemic as it has to persecuting activists, untold numbers of lives could have been saved," he added.
Chinese authorities were also singling out individual activists, the New York-based rights watchdog said.
China identified its first AIDS case in 1985, in a dying tourist. The first indigenous cases were detected four years later in an outbreak involving around 150 heroin users in the southern province of Yunnan.
Those numbers grew to 650,000 HIV or AIDS cases at the end of 2005, according to official statistics, which many experts consider to underplay the true scale of the problem.
Unsafe sex was recently recognized as the leading cause of new HIV cases in China for the first time, overtaking the use of shared intravenous needles.