The pyrazole compound 1-acetyl-3,5-di(4-methylphenyl)-1H-pyrazole, (C19H18N2O), was characterized by X-ray single crystal diffraction technique, IR-NMR spectroscopy and quantum chemical computational methods as both experimental and theoretically. The compound crystallizes in the monoclinic space group C 2/c with a = 32.5334 (1) angstrom, b = 5.8060 (1) angstrom, c = 23.6519 (8) angstrom, beta = 134.572 (2)degrees, and Z = 8. The molecular geometry was also optimized using the Hartree-Fock (HF) and density functional theory (DFT/B3LYP) methods with the 6-311G(d,p) basis set and compared with the experimental data. To determine conformational flexibility, molecular energy profile of the tittle compound was obtained by semi-empirical (AM1) with respect to selected degree of torsional freedom, which was varied from -180 degrees to +180 degrees in steps 10 degrees. From the optimized geometry of the molecule, vibrational frequencies, gauge-independent atomic orbital (GIAO) H-1 and C-13 NMR chemical shift values, molecular electrostatic potential (MEP) distribution, non-linear optical properties, frontier molecular orbitals (FMOs) of the title compound have been calculated in the ground state theoretically. The theoretical result showed good agreement with the experimental values (C) 2012 Elsevier B.V. All rights reserved.