The protesters, from the Ukrainian women's rights group Femen, shouted "Basta (Enough) Berlusconi", as the media tycoon was voting in a polling station in a Milan school.
They were topless and the same words were painted on their bodies. Police quickly grabbed the women and bundled them away.
Mr Berlusconi, who is seeking his fifth term in government, is on trial for having sex with an underage prostitute during alleged "bunga bunga" orgies at his Milan villa, a charge he denies.
The 76-year-old billionaire, pushed out of power in November 2011 as Italy faced a grave financial crisis, enrages feminists who accuse him of exploiting scantily-clad showgirls on his television shows and degrading women with off-colour jokes.
During the election campaign his centre-left rival Pier Luigi Bersani accused him of treating women like inflatable dolls.
An Italian woman has demanded an apology after he made suggestive remarks to her while they were on stage together at a business event.
He says he holds women in high respect and he does not mean to offend anyone with his jokes.