The spin relaxation dynamics of Ce 3+ ions in heavily cerium-doped YAG crystals is studied using pulse-electron paramagnetic resonance and time-resolved pump-probe Faraday rotation. Both techniques address the 4f ground state, while pump-probe Faraday rotation provides also access to the excited 5d state. We measure a millisecond spin-lattice relaxation time T1, a microsecond spin coherence time T2 and a ∼ 10 ns inhomogeneous spin dephasing time T * 2 for the Ce 3+ ground state at low temperatures. The spin-lattice relaxation of Ce 3+ ions is due to modified Raman processes involving the optical phonon mode at ∼ 125 cm −1 . The relaxation at higher temperature goes through a first excited level of the 2 F 5/2 term at about ω ≈ 228 cm −1 . Effects provided by the hyperfine interaction of the Ce 3+ with the 27 Al nuclei are observed.