We have applied two-color resonant two-photon mass analyzed threshold ionization (MATI) spectroscopy to investigate the ionic properties of the structural isomers of methylaniline. The adiabatic ionization energies of o-, m-, and p-methylanilines have been determined to be 61002 +/- 5, 61059 +/- 5, and 60160 +/- 5 cm(-1), respectively. These vibrationally resolved spectra provide information about the active normal vibrations of the corresponding cations. The observed spectral features have been successfully assigned oil the basis of comparison with the results from ab initio and density functional calculations and experimental data available in the literature. The results suggest that both the nature of the substitutents and the relative location in the ring can influence the electronic transition, ionization. and molecular vibration for these structural isomers.