Italy declared war on Austria-Hungary and Germany.
Italy declared war among Austria-Hungary on May 23rd,1915 during World War I.Italy declared war among Germany on October 13th, 1943, making them join the battle on the Allies side.
Italy has also declared war on:
May 23rd 1915 - Austria-Hungary
June 10th 1940 - United Kingdom
June 10th 1940 - France
December 11th 1941 - United States
October 13th 1943 - Germany