More than 20 Burmese student leaders detained by the authorities on Friday have been released.
They were held ahead of the anniversary of the suppression of a student movement 50 years ago.
About 300 people met in Rangoon to mark the event despite the detentions and the presence of plain-clothes police.
Activists say the detentions prove that the Burmese military still has repressive tendencies, despite recent reforms.
7 July is the 50th anniversary of the Burmese military's brutal suppression of student demonstrations, just four months after a coup by Gen Ne Win which began almost five decades of repressive rule.
Dozens were killed - and the following day the student union building at Rangoon University was dynamited.
"Police officials told us that they just wanted to question us in connection with our plans to commemorate the anniversary," All Burma Students Union Phyo Phyo Aung told the Reuters news agency.
Activists said the detentions were made in several different locations across the country, including five in Rangoon.
Activist Ko Ko Gyi said some of those detained had been released under an amnesty for political prisoners several months ago.
Hundreds of political prisoners have been released in the last year as part of the reforms.