The EPR spectra of Gd3+ ion replacing Y3+ or rare-earth (RE) ions in aluminum borates REAl3(BO3)4 (RE = Y3+, Eu3+, Tm3+) have been studied. The spin-Hamiltonian parameters of an impurity Gd3+ ion in these crystals were determined. The basic atom coordinates in the structure of TmAl 3 (BO3)4 crystal have been established. Distortions of the Gd3+ ion nearest environment were analyzed within the framework of the superposition model of zero-field splitting. The parameter change in isomorphic aluminum borates is shown to be determined by change of the angle between the Gd3+O2− bond and the C3-axis.