A new 5-methyl-2-hydroxy-acetophenone-thiosemicarbazone ligand (L) and its nickel(II) complex [Ni(L)(PPh3)] were synthesized. The crystal structure of free ligand and its complex has been determined by single crystal X-ray diffraction technique. In the complex, thiosemicarbazone ligand is coordinated to nickel through ONS mode. The structures were also characterized by elemental analysis, IR, H-1 NMR and UV-Vis. spectroscopies. In addition, the molecular geometries, vibrational frequencies and gauge independent atomic orbital (GIAO) H-1 NMR chemical shift values of the compounds in the ground state have been calculated using the density functional theory (B3LYP) method with 6-311G(d,p) basis set for C, H, N, O, P, S atoms and LANL2DZ basis set for Ni atom. Electronic transitions were calculated using the time-dependent density functional theory (TD-DFT) formalism and the experimental spectra of the compounds have been discussed. (C) 2015 Elsevier Ltd. All rights reserved.