The men are among six lesbian and gay activists who were formally charged with the public order offence on October 7th following a police investigation into a protest held in the city of Perugia in March.
Human Rights Watch on Thursday described the charges as reflecting prejudiced attitudes and urged Perugia's prosecutors to drop them.
"They would be laughable if they didn't reflect exactly the anti-gay sentiment the activists are fighting," said HRW's Judith Sunderland.
The demonstration which landed the six in trouble was a counter protest to one by a group called Sentinelle in Piedi (Standing Sentries) which is opposed to gay unions and the extension of anti-discrimination legislation to include homosexuals.
The police report on which the charges are based accuses the activists of calling their opponents "fascists" and "bigots" and highlights their "colourful" clothing as well as the kiss.
It states that after being asked to move on, the two men had engaged in "a long and passionate kiss on the mouth…in front of many families with children and teenagers, many of them minors, leaving passersby disgusted at such a display."
Four of the six activists have also been charged with staging an illegal demonstration.
"Gay men and lesbian women kissing public is not a crime," HRW's Sunderland said. "The activists' actions are clearly protected by their right to peaceful protest."
The Perugia case comes against a background of heightened tensions in Italy over the treatment of same-sex couples.
The Sentries movement staged prayer vigil-style demonstrations in dozens of towns and cities on October 5th over government plans to authorize civil unions for same-sex couples.
Counter-demonstrations led to scuffles and arrests in a number of cities but no charges were brought.
Prime Minister Matteo Renzi has promised to introduce legislation to allow gay couples to have legally-enshrined partnerships by January.
The government has no plans to follow other European countries by according homosexuals the right to marry, which a majority of Italians oppose.
A number of towns and cities have registered the marriages of gay couples married outside of Italy but Interior Minister Angelino Alfano ordered them to stop the practice earlier this month, saying it had no legal basis.
Some mayors have vowed to defy the order, including Rome's Ignazio Marino, who registered 16 gay marriages on Saturday.