In this work, 4-allyl-5-(thiophen-2-ylmethyl)-2H-1,2,4-triazol-3(4H)-one has been synthesized and characterized by using FT-IR, H-1 NMR. UV-vis spectra and XRD (X-ray single crystal determination) experimentally and using B3LYP/6-31G(d), HF/6-31G(d) methods theoretically. The structure of compound is stabilized by two intermolecular hydrogen bonds and by intermolecular C-H center dot center dot center dot pi interaction. The molecular geometry, vibrational frequencies and Gauge Including Atomic Orbital (CIAO) 1H chemical shift values of the title compound in the ground state have been calculated using the density functional (B3LYP) and HF method with the 6-31G(d) basis set. The calculated results show that the optimized geometry parameters, the theoretical vibrational frequencies and chemical shift values show good agreement with experimental values. In addition, Mulliken atomic charges of the title compound were calculated and discussed. Besides HOMO-LUMO energy gap, molecular electrostatic potential map and electronic absorption spectra were performed at B3LYP/6-31G(d) level of theory and transition states were also mentioned. (C) 2012 Elsevier B.V. All rights reserved.