We report mechanoluminescence (ML) in Sm3+-doped Sr3Sn2O7 phosphors with perovskite-related structure. The ML from Sr3Sn2O7:Sm3+, emitted strong reddish-orange light upon compression, is clearly observable by naked eyes. Based on the comparison between ML spectrum and photoluminescence spectrum, the ML emission was identified to be due to electron transition from an excited state 4G5/2 to the ground state 6HJ (J = 5/2, 7/2, 9/2) in Sm3+ ions. Although the ML emission was gradually decayed as compressive load was applied repeatedly, it recovered completely upon irradiation with UV light (254 nm). This behavior indicating that ML of Sr3Sn2O7:Sm3+ is intimately related to the charge traps. The charge transfer state (CTS) band in the PL excitation spectra was observed for Sr3Sn2O7:Sm3+, indicating that the efficient energy transfer from the host to the Sm3+ ions. The formation of CTS and the charge traps may be responsible for this ML performance.