M121 or M-121 may refer to:
M121/A1 155mm Cartridge, a U.S. Army chemical artillery shell M-121 (bomb), a World War II bomb M121 mortar carrier, the United States designation for the Soltam TT6 M-121 highway (Michigan), a road connecting Zeeland and Grandville Mauboussin M.121 Corsaire Major, a 1921 French trainer and touring aircraft M121 (Cape Town), a Metropolitan Route in Cape Town, South Africa