Objective To study the intervention and mechanism of glycogen synthase kinase 3 (GSK3) inhibitor, lithium chloride, on the elevated plus-maze behavior of fragile X mental retardation 1 (FMR1) knockout mice. Methods Ninety 30-days-old FMR1 knockout (KO) mice were used in this study and lithium chloride was intraperitoneally and continuously injected for 5 days. Elevated plus-maze test was processed in day 6. We monitored the trace of the mice and analyzed it with a software named Smart, to observe whether lithium chloride could ameliorate the phenotype of KO mice in elevated plus-maze. We also tested the expression of GSK3β and p-GSK3β in both cortex and hippocampus of KO and wild type (WT) mice with Western blotting. Results In the elevated plus-maze, we observed that, comparing with WT mice, KO mice had significantly higher moveability, excitability and exploratory. KO mice also had more time spent in open arms as well as the entry and total distance than WT mice. After lithium chloride administration, the time spent, entry and total distance of KO mice in the open arms had significantly reduction (EM>P/EM> <0.05). In Western blotting test, we found the expression of p-GSK3β of KO mice was less than WT mice. After treated with lithium chloride, KO mice had the increased p-GSK3β expression. WT mice had amelioration in time spent, entry and total distance in the open arms after lithium chloride applied. We observed the increased p-GSK3β expression in the lithium chloride treated WT mice. Compared the KO control with the WT control, there was no significant difference in total GSK3βexpression.After lithium chloride administration, there were no significance changes in total GSK3β expression (P >0.05).Conclusion The function of lithium which ameliorates elevated plus-maze behaviors