"Following the well-known events of recent days, it seems opportune to delay the event," the Vatican said in a statement Tuesday.
Students at Sapienza University cheered at the news of the rare cancellation of a papal appearance, The New York Times said. Students and professors had rallied against the pope's appearance citing a 1990 speech he gave calling the church's condemnation of Galileo "rational and just." The church condemned the scientist in the 1600s for saying the Earth revolved the sun.
Some politicians decried the decision to cancel the speech at the university.
"No voice should be stifled in our country, least of all the pope's," Italian Prime Minister Romano Prodi said.