[en] The relaxation rate of europium ions in europium ion garnet (EuIG) was estimated by assuming that the crystal field is modulated by optical phonons. Mixing J = 2 states into the J = 0 and J = 1 states by the static rhombic field, breaks the 'triangle selection rule' and makes possible this mechanism. It is concluded that the mechanism proposed here can be responsible for the order of magnitude of the line width in the ferromagnetic resonance of EuIG, but to obtain the observed isotropy of the line width, it is necessary to make rather arbitrary assumptions concerning the dependence of phonon spectral density on frequency