Objective:To evaluate the inhibitory effects of norcantharidine(NCTD) on ovarian carcinoma 3AO and AO cells cultured in vitro and to reveal its mechanism.Methods:Using cell culture technique,the inhibitory effects of NCTD on 3AO and AO cells were measured by way of crystal violet dyeing.The alterations of cell cycle induced by NCTD were analyzed with flow cytometry.Results:3AO and AO cells exposed to NCTD 1 μg/ml were inhibited slightly.The IC50 values of NCTD for them were 20 μg/ml and 10 μg/ml respectively.The growth of 3AO and AO cells was inhibited after being cultured with NCTD for 6 h. The inhibitory rates were increased as time of culture prolonged.The percent age of 3AO and AO cells in G2+M phase were increased obviously and the percentage of cells in S phase were decreased accordingly after treated with NCTD. Conclusion: NCTD has a significant inhibition of ovarian carcinoma 3AO and AO cells,which is in a dose- and time-dependent manner. The mechanism of NCTD-induced antiproliferative effect appears to involve blockade of tumor cells in the G2+M phase of the cell cycle.