The Izu peninsula (伊豆半島, Izu-hantō^?) is a large mountainous peninsula with deeply indented coasts to the west of Tokyo on the Pacific coast of the island of Honshū, Japan. Formerly the eponymous Izu Province, Izu peninsula is now a part of Shizuoka Prefecture. The peninsula has an area of 1,421.24 km² and its estimated population in 2005 was 473,942 persons.

Tectonically, the Izu peninsula results from the Philippine Sea Plate colliding with the Okhotsk Plate at the Nankai Trough. The Philippine Sea Plate, the Amurian Plate, and the Okhotsk Plate meet at Mount Fuji.

The southern portion of the peninsula is composed largely of breccia, and the central and northern portions consist of numerous highly eroded volcanos. The Amagi Mountain Range dominates the center of the peninsula with Mount Amagi (1406 m) and Mount Atami (773 m) in the east and Mount Daruma (982 m) in the west, with the eastern and western portions of the range extending underwater into Sagami Bay and Suruga Bay. The peninsula's major river, the Kano River in the north, flows through a graben valley created by plate tectonics.