Boso Peninsula (房総半島 Bôsô-hantô) is a peninsula in Chiba prefecture on Honshu, the largest island of Japan, forming the eastern edge of Tokyo Bay, separating it from the Pacific Ocean. Most of the peninsula is hilly, with some points as high as 400 m above sea level. While the western part of the peninsula is highly urbanized (centered around the city of Kisarazu), the other coastal lowlands and interior river valleys are chiefly used for growing rice.

The Tokyo Wan Aqua-Line, a bridge-tunnel across Tokyo Bay, connects Kisarazu and the city of Kawasaki in Kanagawa Prefecture.

The peninsula gets its name (and the kanji) from the former provinces that were located there: Awa (安房) contributed the first kanji while Kazusa　(上総) and Shimosa (下総) contributed the second.