The Balkan outfit have been the outstanding side of the London 2012 tournament, with eight wins from eight matches, and end it as worthy champions.
Their dominance in defence was too much for the Italians, who are reigning world champions.
Miho Boskovic, who scored twice in the victory, said: 'We played amazing the whole tournament. So I think we deserve 100 per cent this medal.
'We played the best Water Polo and did an outstanding performance in the last match.'
Earlier, Serbia won bronze by coming from behind to beat rivals Montenegro 12-11.