Y21 may refer to:
Rail station codes in Japan Ikoma-Sanjō Station, in Ikoma, Nara Minoura Station, in Kan'onji, Kagawa Numanosawa Station, in Yūbari, Hokkaidō Suminoekōen Station, in Suminoe-ku, Osaka Tsukishima Station, in Chūō, Tokyo Yasuura Station, in Kure, Hiroshima
Other uses Bandy World Championship Y-21 , a sloop of the Royal Navy