Methyl salicylate (MS) as a subunit of larger salicylates found in commercial sunscreens has been shown to exhibit keto-enol tautomerization and dual fluorescence emission via excited-state intramolecular proton transfer (ESIPT) after the absorption of ultraviolet (UV) radiation. However, its excited-state relaxation mechanism is unclear. Herein, we have employed the quantum mechanics(CASPT2//CASSCF)/molecular mechanics method to explore the ESIPT and excited-state relaxation mechanism of MS in the lowest three electronic states, that is, S-0, S-1, and T-1 states, in a methanol solution. Based on the optimized geometric and electronic structures, conical intersections and crossing points, and minimum-energy paths combined with the computed linearly interpolated Cartesian coordinate paths, the photophysical mechanism of MS has been proposed. The S-1 state is a spectroscopically bright (1)pi pi* state in the Franck-Condon region. From the initially populated S-1 state, there exist three nonradiative relaxation paths to repopulate the S-0 state. In the first one, the S1 system (i.e., ketoB form) first undergoes an ESIPT path to generate an S-1 tautomer (i.e., enol form) that exhibits a large Stokes shift in experiments. The generated S-1 enol tautomer further evolves toward the nearby S-1/S-0 conical intersection and then hops to the S-0 state, followed by the backward ground-state intramolecular proton transfer (GSIPT) to the initial ketoB form S-0 state. In the second one, the S-1 system first hops through the S-1 -> T-1 intersystem crossing (ISC) to the T-1 state, which then further decays to the S-0 state via T-1 -> S-0 ISC at the T-1/S-0 crossing point. In the third path, the T-1 system that stems from the S-1 -> T-1 ISC process via the S-1/T-1 crossing point first takes place a T-1 ESIPT to generate a T-1 enol tautomer, which can further decay to the S-0 state via T-1-to-S-0 ISC. Finally, the GSIPT occurs to back the system to the initial ketoB form S-0 state. Our present work could contribute to understanding the photophysics of MS and its derivatives.