Monthly Shōnen Sirius (Japanese: 月刊少年シリウス, Hepburn: Gekkan Shōnen Shiriusu) is a Japanese monthly shōnen manga magazine published by Kodansha, and first issued in May 2005. It is issued in perfect-bound B5 format and retails for 580 yen. Like all monthly shonen manga magazines, Monthly Shonen Sirius is aimed at late teens and people in their early 20s from ages 16 to 21.