The activists' detention sparked outrage among LGBT rights groups in the country.
Rights activist Nikita Safronov told AFP that he and four other people, including Italian national Yuri Guaiana, were taken into police custody as they were walking toward the headquarters of the Russian Prosecutor General.
"We were bringing a request and petition signatures so that they investigate the crime against the LGBT in Chechnya," Safronov said.
Later Thursday all of them were released, they said.
The Moscow police and the prosecutor general's office could not be reached for comment.
Safronov said they were carrying 10 empty large boxes and had planned to deliver them to the prosecutor general's office -- which they said was a symbolic act meant to show the petition had received two million signatures.
"They symbolised the number of signatures we had," Safronov said. "We aren't crazy. didn't plan on wasting 100 kilos of paper."
Student Alexandra Alexeyeva, who was among those detained, told AFP they had also planned to hand a USB key containing the petition, which was launched after reports of a campaign against gays in Chechnya.
President Vladimir Putin last week backed an official probe into reported brutal attacks on gay men in Chechnya after German Chancellor Angela Merkel confronted him on the issue, promising to "talk to the Prosecutor General".
The activists' detention sparked outrage among LGBT rights groups.
"Arresting activists for simply trying to deliver those names is outrageous and deeply worrisome, as it shows that Putin's administration would prefer shutting down our voices instead of imparting justice," Kate Staff, acting executive director of the LGBT right group All Out, said in a statement.
Arcigay, Italy's leading gay rights group, on Thursday slammed "Russian institutions' intolerable hostility toward LGBTI people."
In March, the Novaya Gazeta opposition daily reported that Chechen authorities were imprisoning and torturing gay men in the conservative region where homosexuality is taboo.
A group of Chechen men in a safe house near Moscow later confirmed to AFP that they had fled the region in fear of their lives after being beaten and imprisoned.