The ESR of Cr3+ in phosphate, fluorophosphate and fluoride glasses has been studied. The effective g factors of Cr3+ have been calculated with the Spin-Hamil-tonian. It is pointed out that the low-field spectra resulted mainly from transition between two Kramers doublets. Hamiltonian parameters have been determined: D=0.15-0.4 cm-1, E/D=0.15-0.3; zero-field splitting: 0.3-0.8 cm-1. In this paper, the ESR of Mo3+ ion in phosphate glass is also reported.