Abstract: The spin Hamiltonian parameters g//, g⊥, A// and A⊥ for the two Cu2+-Vc centers I2 and II4 in NH4I at room temperature are theoretically studied by means of diagonalization procedure of complete (10x10) energy matrix (DPCEM) for a 3d9 ion in tetragonal symmetry. Based on the calculations, the nearest ligand I-intervening in the impurity Cu2+ and the second (or fourth) neighbour cation vacancy Vc are found to be displaced towards the impurity by about 0.15Å (or 0.14Å) for centers I2 and II4, respectively.