X-band (approximate to 9.8 GHz) electron paramagnetic resonance (EPR) measurement at ambient temperature in three mutually perpendicular planes have been carried out on a single crystal of Cu2+ doped mixed ligand complex of Ni(II) with saccharin and nicotinamide [Ni(Nic)2(H2O)4](sac)2. The angular dependent spectra showed that the Cu2+ ion enters Ni2+ sites in the lattice and distorted local environment of Ni2+ site. The principal g and A values, covalency parameter (alpha '(2)), mixing coefficients (alpha and beta) and Fermi contact term (K) have been evaluated from the EPR analysis. The ground-state wave function of the Cu2+ ion has been constructed using the alpha '(2), alpha and beta values. The nature of the distortion present in the lattice is obtained from the values of the mixing coefficients. (c) 2005 Elsevier B.V. All rights reserved.