ESR studies of Fe3+ centers in Na3H(SO4)2, crystals revealed that the sodium ion vacancies are the charge compensating vacancies. Fe3+ ion is trapped at two physically distinct sites and the overall symmetry is not much affected due to the charge compensating vacancies. The data are fitted to the most general spin Hamiltonian by the method of least squares and the spin Hamiltonian parameters are reported. © 1983.