In this paper the spin-Hamiltonian parameters, g factors g(parallel to), g(perpendicular to) and zero-field splittings b(2)(0), b(4)(0), b(4)(4), b(6)(0), b(6)(4), for Gd3+ ion in molybdates AMoO(4) (A = Ca, Sr, Ba, Pb) are calculated by a diagonalization (of energy matrix) method based on one-electron crystal field mechanism. The crystal field parameters in the matrix are calculated from the superposition model. The results indicate that seven calculated spin-Hamiltonian parameters are in good agreement with the experimental values by using only three reasonable adjustable parameters (i.e., the intrinsic parameters (A) over bar (k)(R-0), where k = 2, 4, 6, in the superposition model). It is shown that the diagonalization method can be used to calculate and explain the spin-Hamiltonian parameters of Gd3+ ion in crystals. The results are discussed.