The electron paramagnetic resonance (EPR) of Gd3+ in MgF2 reveals that Gd3+ has two different environments in the lattice. One of them has D 2h symmetry, the EPR spectrum is characterized by a large zero field splitting [B 2 0 = 968.10−4 cm−1; B 2 2 = 357.10−4 cm−1] and the fourth order term of the spin Hamiltonian is axial; it is assumed that one Gd3+ substitutes two Mg2+. The other Gd3+ center has only monoclinic symmetry. From the analysis of the fourth order term of the spin Hamiltonian of the corresponding spectrum it is seen that one Gd3+ substitutes one Mg2+ and that this substitution produces a large local distortion of the lattice.