The S1←S0 electronic transition and threshold ionization of the cis and trans rotamers of mmethylanisole were investigated by using one-color resonant two-photon ionization and mass-analyzed threshold ionization techniques. The first electronic excitation energies (E1) of the cis and trans rotamers were determined to be (36049 ± 2) and (36117 ± 2) cm-1 , while the adiabatic ionization energies (Ip) were (64859 ± 5) and (65110 ± 5) cm-1 , respectively. The results of ab initio and density functional theory calculations provide a satisfactory interpretation for our experimental findings concerning the difference in the transitional energies of the cis and trans rotamers and assist in assigning the vibronic and cation spectra obtained in the present study. The observed active vibrations of both rotamers in the S1 and D0 states primarily consist of methyl torsion, in-plane ring deformation, and substituent-sensitive bending modes. Both experimental and theoretical results show that, for both cis and trans isomers, the geometry of the cation in the D0 state is somewhat different from that of the neutral species in the S1 state. In addition, the strengths of both the through-space substituent-substituent and substituent-ring interactions were found to follow the order: S0