In this study, the structural and spectroscopic investigations of 3-methyldiphenylamine were reported. The molecular geometry was optimized from Density Functional Theory (B3LYP method) using 6-31+G(d,p) basis set on the ground state and the infrared wave-numbers and intensities were predicted by using this geometry. Calculated wavenumbers and intensities were compared with FT-IR spectrum of 3-methyldiphenylamine. Additionally, time depended density functional theory (TD-DFT) method using 6-31++G(d,p) basis set was used to determine the minimum energy structure of 3-methyldiphenylamine. According to the calculated results, the vibrational wavenumbers and excitation energies show an excellent agreement with the experimental data. Furthermore, these calculated results can be employed to predict the vibrational and electronic properties for improving organic semiconductor materials. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.