Their faces covered with pink balaclavas and shouting "Blood is Russia's art" and "Disobey," 50 members of feminist groups opposed to Russian President Vladimir Putin blockaded the highly controversial pavilion for at least half an hour while Italian police prevented them from getting inside.
They chanted, played a punk rock song and dispersed without confrontation.
After years of war, "you guys just opened the door to them," said Pussy Riot founder Nadya Tolokonnikova, adding the Biennale had not comprehended the importance of "so-called soft power, things, things that seemingly for some people are not important or not political."
"For Russia, it's clear that it's part of their military strategy, and that's the way they try to conquer the West," she said.
This year is the first time Russia has participated in the international art exhibit since its 2022 full-scale invasion of Ukraine.
The opening has already cost the Biennale two million euros ($A3.2 million) in EU funding, and plunged the normally serene week of previews into chaos after the jury resigned in protest of both Russia and Israel's participating, citing crimes against humanity.
The Biennale has defended its decision saying any country with relations with Italy is free to participate in the exhibition, despite opposition from Premier Giorgia Meloni's government.
The protest comes on the second day of VIP previews for art world luminaries and journalists ahead of the Biennale's opening on Saturday.
The run-up to Biennale's 61st edition is the most contested in recent memory, reflecting global turmoil that is spilling over into the exhibition that features 100 national pavilions and 110 artist and artist groups participating in the main curated exhibition titled In Minor Keys.
Palestinians also protested Israel's participation with actions in the Giardini.
On Wednesday, a separate group of protesters descended on the Israeli exhibit, leaving the floor outside carpeted with rain-sodden leaflets denouncing a "Genocide Pavilion".
Last week, the entire international jury resigned after a statement that referred to countries with leaders wanted by the ICC for suspected war crimes. It meant Russia and Israel.
with DPA
