The 42-year-old activist, who allegedly jumped over a small steel fence in front of the embassy on Friday, was quickly overpowered by Japanese police and arrested.
A Tokyo police spokesman confirmed the release of Wu'er, now a Taiwanese citizen, but declined to give further details. He spoke on condition of anonymity, citing department policy.
Wu'er was No. 2 on China's list of 21 wanted student leaders after the crackdown on the protesters, in which at least hundreds of people were killed. He escaped and has lived in exile in Taiwan, where he has been a businessman and political commentator.
Wu'er gained attention as a pajama-clad hunger striker haranguing then Chinese Premier Li Peng at a televised meeting during the protests in Beijing.
As he walked out of a police detention facility, he told Japanese broadcaster TBS that he tried to run into the embassy to "request a dialogue" with the Chinese government.
He also said in the interview that he wanted to return to China to be arrested, if that's the only way he could see his aging parents.
"For 21 years I haven't been able to see my parents. It's so sad," Wu'er said. "I've been making efforts to return to my country since last year." Japanese media reports said he tried to get a flight to Beijing ealier this month but was rejected, contributing to his motive Friday.
Wu'er could not be immediately reached for comment.
China has never fully disclosed what happened when its military crushed the weekslong, student-led protests on the night of June 3-4, 1989.
Beijing has long maintained that the protests were a "counterrevolutionary riot," and public discussion or displays referencing them remain forbidden on the mainland.
