In the present study, Fmr1 knockout mice (KO mice) were used as the model for fragile X syndrome. The results of step-through and step-down tests demonstrated that Fmr1 KO mice had shorter latencies and more error counts, indicating a leing and memory disorder. After treatment with 30, 60, 90, 120, or 200 mg/kg lithium chloride, the leing and memory abilities of the Fmr1 KO mice were significantly ameliorated, in particular, the 200 mg/kg lithium chloride treatment had the most significant effect. West blot analysis showed that lithium chloride significantly enhanced the expression of phosphorylated glycogen synthase kinase 3 beta, an inactive form of glycogen synthase kinase 3 beta, in the cerebral cortex and hippocampus of the Fmr1 KO mice. These results indicated that lithium chloride improved leing and memory in the Fmr1 KO mice, possibly by inhibiting glycogen synthase kinase 3 beta activity.