X-band single-crystal electron paramagnetic resonance (EPR) studies of the molecular alloy [NO(2)BzPy][Au0.57Ni0.43(mnt)(2)] are presented in this paper. At room temperature, EPR spectra show both intense resonance signals (main signals) and weak satellite quartet lines. The characteristics of both intense and weak EPR signals depend on the magnetic field orientation. The main signals arise from two magnetically nonequivalent [Ni(mnt)(2)](-) anions, and their corresponding. principal values of the g tensor are (g(x)')(1) = 2.04653, (g(y)')(1) = 2.00096, and (g(z)')(1) = 2.15319 and (g(x)')(2) = 2.04520, (g(y)')(2) = 1.99734, and (g(z)')(2) = 2.15361, respectively. The weak satellite lines, whose patterns strongly depend on the magnetic field direction, can be attributed to the hyperfine coupling of the electron spin with the Au-197 nucleus of the [Au(mnt)(2)](-) species. Density functional theory calculations for the spin and charge distributions of the dimer {[Ni(mnt)(2)] [Au(mnt)(2)]}(2-) indicate that the hyperfine interaction of the electron spin with the 197 Au nuclear spins is caused, in part, by the charge transfer between the [Ni(mnt)(2)](-) and the [Au(mnt)(2)](-) species.