Mae Sai is home to the district headquarters of Mae Sai District in the top of Chiang Rai province, Thailand.

Mae Sai may also refer to:

• Mae Sai District, Chiang Rai province, northernmost district of Thailand
• Mae Sai Subdistrict, subdistrict of Mae Sai District
• Mae Sai River
• Mae Sai, Phayao, subdistrict of Mueang Phayao district, Phayao province, Thailand