Abstract： Objective To observe the effect of lovastatin on the excitotoxicity induced by NMDA in cortical neurons in rats and to investigate the underlying mechanism. Methods Cortical neurons prepared from E17 rats were assigned into 4 groups:NMDA group (addition of 100 μmol/L of NMDA for 15 minutes),LOV group (pretreatment of the neurons for 3 days with 500 nmol/L of LOV),LOV+NMDA group (pretreatment of the neurons for 3 days with 500 nmol/L of LOV and addition of 100 μmol/L of NMDA for 15 minutes) and untreated group (addition of isodose solvent).Cell viability was evaluated with the trypan blue dye exclusion test,the morphology and number of neurons were assessed with MAP-2 immunofluorescence staining,and the level of protein was measured with Western blotting assay. Results Trypan blue staining demonstrated that the pretreatment with 500 nmol/L of lovastatin for 3 days significantly protected the neurons against the excitotoxicity induced by NMDA (P＜0.05 vs NMDA).Immunofluorescence staining demonstrated the number of MAP-2 positive neurons decreased and the surviving neurons showed a loss of MAP-2 positive dendrites after NMDA treatment (P＜0.05 vs untreated),which were not observed after lovastatin pretreatment (P＜0.05 vs NMDA).Excitotoxicity was mediated in part by the Calpain over-activation and the subsequent protein truncation events on Calpain substrate, CDK5 co-activator P35 to P25 cleavage. Lovastatin pretreatment remarkably suppressed Calpain over-activation and the conversion from P35 to P25 in response to NMDA exposure as detected by Western blotting analysis (P＜0.05 vs NMDA). Conclusions Lovastatin significantly attenuates the excitotoxicity induced by NMDA. The neuroprotection of lovastatin may be mediated by blocking the Calpain and CDK5 over-activation.