Musashi Province (武蔵国, Musashi no Kuni; Japanese pronunciation: [mɯꜜ.sa.ɕi (no kɯ.ɲi)]) was a province of Japan, which today comprises Tokyo Metropolis, most of Saitama Prefecture and part of Kanagawa Prefecture. It was sometimes called Bushū (武州). The province encompassed Kawasaki and Yokohama. Musashi bordered on Kai, Kōzuke, Sagami, Shimōsa, and Shimotsuke Provinces.

Musashi was the largest province in the Kantō region.

Musashi had its ancient capital in modern Fuchū, Tokyo, and its provincial temple in what is now Kokubunji, Tokyo. By the Sengoku period, the main city was Edo, which became the dominant city of eastern Japan. Edo Castle was the headquarters of Tokugawa Ieyasu before the Battle of Sekigahara and became the dominant city of Japan during the Edo period, being renamed Tokyo during the Meiji Restoration.

Hikawa-jinja was designated as the chief Shinto shrine (ichinomiya) of the province; and there are many branch shrines.

The former province gave its name to the battleship Musashi of the Second World War.

Musashi Province had 21 districts and then added one later.