The optimized molecular structures of cis and trans m-cresol in the ground S 0 , electronically excited S 1 , and cationic D 0 states are predicted by ab initio and density functional theory (DFT) calculations. Their vibrational spectra in the S 1 and D 0 states are recorded by two color resonant (1+1′) two photon ionization (2C-R2PI) and mass analyzed threshold ionization (MATI) methods. In consideration of the optimized geometries, the trans rotamer is more stable than the cis one in the S 0 state. Upon the S 1 ←S 0 excitation, the aromatic ring expansion is expected, and the interaction of the OH group with the ring is enhanced. On the D 0 ←S 1 transition, the bond length of the C1–O7 bond is further shortened, exhibiting a partial double bond character in the D 0 state. The band origins of cis and trans m-cresol are measured to be 35,982±2 and 36,098±2cm −1 by the 2C-R2PI method, and their adiabatic ionization energies (IE) are determined to be 66,933±5 and 67,084±5cm −1 by the MATI technique. Comparison of the IE of o-, m-, p-cresol, and phenol gives the order as: p<o<m<phenol. Analysis of the spectroscopic features of cis and trans m-cresol in the S 1 and D 0 states shows that different orientations of the OH group with respect to the CH 3 group slightly influence the vibrational frequency of the in-plane ring deformation.