Al-doped B 4 C was synthesized by high temperature solid-state sintering of carbon, boron and aluminum powders at 2200°C. Results of X-ray diffraction and Raman spectroscopy of the products revealed that the Al atoms had entered the B 4 C lattice. The AC susceptibilities of Al-doped B 4 C which measured at different frequencies exhibited temperature-dependence. And the freezing temperatures shifted to higher value as the driving frequency increased. The finding was consistent with the features of a canonical spin glass. It consequently demonstrated that our prepared Al-doped B4C sample was a spin glass system.