The resonance Raman spectroscopy in conjunction with the density functional theory calculations were used to study the excited state structural dynamics of 2-mercapto-1-methylimidazole (MMI). The experimental UV absorption bands were assigned according to the time-dependent density functional calculations. The vibrational assignments were done for the A-band resonance Raman spectra of MMI in water and acetonitrile on the basis of the Fourier transform infrared (FT-IR) and FT-Raman measurements in solid, in water and in acetonitrile and the corresponding B3LYP/6-311+G(d, p) computations. The dynamic structures of MMI were obtained by analysis of the resonance Raman intensity pattern and normal mode analysis. The differences in the dynamic structures of MMI and thiourea were revealed and explained. The structural dynamic of MMI was found to be similar to that of 2-thiopyrimidone in terms of major reaction coordinates and thus favored the intra-molecular proton transfer reaction. Copyright © 2012 John Wiley & Sons, Ltd.