Italy is obliged to let him enter under accords with the Vatican, which is legally a separate state.
Mr Mugabe is a Catholic and often attends Mass in Harare’s cathedral.
The trip was denounced by one of his leading critics – the Archbishop of Bulawayo, Pius Ncube. Mr Mugabe’s party is accused of rigging last week’s poll.
Mr Mugabe and about 100 of his associates were banned from the EU and the US after being accused of using fraud and violence to ensure victory in the 2002 presidential election.
He has nevertheless attended several international summits in both EU countries and the US.