Magnetic characterization was performed on the Al-doped monoclinic phase of LiMnO 2 stabilized by high-temperature firing in reducing atmosphere. Curie and Weiss constants (C=0.0315emuK/gOe, Θ=-566K) obtained in the paramagnetic regime indicate strong antiferromagnetic interactions between the high-spin Mn 3 + ions. Spin-glass behavior is observed at low temperatures, and is attributed to geometrical frustration due to triangular antiferromagnetism and randomness due to Al substitution and cation disorder. Paramagnetic behavior is observed below the spin freezing temperature, indicating the presence of some unfrozen spins.