Marco Carnelos was accompanied by the officials of the Astan during the visit.
He toured different sections of the mausoleum and expressed wonder at the rare historical buildings and items there.
Carnelos has served as Italy’s envoy in Iraq since June 2015.
The holy shrine of Imam Ali (AS) in Najaf, 160 km south of Baghdad, is one of the most sacred sites in Shia Islam.
Millions of Shia pilgrims from around the world visit the holy site every year.