[en] The ESR study of Cu²⁺ doped sodium ammonium sulphate dihydrate has been done at room temperature. Two magnetically inequivalent sites for Cu²⁺ have been observed. The spin-Hamiltonian parameters have been determined with the fitting of spectra to rhombic symmetry crystalline field. The parameters are Cu²⁺ (I): g_x=2.121, g_y=2.138, g_z=2.425, A_x=23x10^-4 cm^-1, A_y=54x10^-4 cm^-1, A_z=92x10^-4 cm^-1; Cu²⁺ (II): g_x=2.038, g_y=2.061, g_z=2.337, A_x=35x10^-4 cm^-1, A_y=57x10^-4 cm^-1, A_z=100x10^-4 cm^-1. The ground state wavefunction has also been determined. The g-anisotropy has been evaluated and compared with the experimental value. With the help of optical study, the nature of bonding in the complex has also been discussed.