Ohi Day (also spelled Ochi Day, Greek: Επέτειος του «'Οχι» Epeteios tou "'Ohi", Anniversary of the "No") is celebrated throughout Greece, Cyprus and the Greek communities around the world on October 28 each year, to commemorate Greek Prime Minister Ioannis Metaxas' (in power from August 4, 1936, until January 29, 1941) rejection of the ultimatum made by Italian dictator Benito Mussolini on October 28, 1940.

This ultimatum, which was presented to Metaxas by the Italian ambassador in Greece, Emanuele Grazzi, on October 28, 1940, at dawn (04:00 am), after a party in the German embassy in Athens, demanded that Greece allow Axis forces to enter Greek territory and occupy certain unspecified "strategic locations" or otherwise face war. It was allegedly answered with a single laconic word: όχι (No!) However, his actual reply was, Alors, c'est la guerre (Then it is war).