The experimental study of the electron spin-lattice relaxation (SLR) of Nd³⁺ and Tb³⁺ ions in phosphate and sodium borate silica glasses was performed. Measurements were made with electron spin echo technique. Temperature dependences of spin-lattice relaxation of the rare earth ions reveal the contribution of different relaxation mechanisms. A stepped like change of the SLR rate observed for Tb³⁺ and Nd³⁺ ions was explained by cross relaxation.