Abstract： [Objective]To investigate and compare the changes of Drebrin A,Drebrin E and lcam-5 mRNA levels in the cerebral cortex of Frr-1 gene knockout mouse during brain development periods.[Methods]Fmr-1 gene knockout (KO) male mice and their wild type (WT) counterparts were chosen in our experiment (4≤n≤ 10);the levels of target mRNAs were detected by real time quantitative PCR;check points were set on the 7th,14th,21th and 28rh postnatal d.[Results] The mRNA level of Drebrin A in the KO group was significantly lower than that in the WT group on the 14th postnatal d,while that of Drebrin E was significantly higher than that in the WT group (P＜0.05).The mRNA level of lcam-5 in the KO group was significantly higher than that in the WT group on the 14th and 21th postnatal d (P＜0.05).[Conclusion] The delayed shift of Drebrin A to Drebrin E and transitional over-expression of lcam-5 in developmental cerebral cortex are the reasons for mental retardation in Fragile X Syndrome.