Objective To investigate the effect of antiCD81(antibodys against CD81) on the proliferation of astrocytes. Methods Purified astrocytes from newborn rats’ cerebral cortex were divided into 6 groups and added with antiCD81 different concentrations(0,0.1，0.5，1,5，10mg/L). The activity of astrocytes was tested by methyl thiazolyl terazolium(MTT). Three significative groups were chosen based on MTT result and added with antiCD81 of different concentrations(0,0.5，5mg/L). After administration for 24 hours, the cell cycle of the astrocytes was measured by flow cytometer. The corresponding data were analyzed with SPSS statistical software. Results 1By MTT, the average optical density(AOD) values of astrocytes were reduced after administration with antiCD81 of different concentrations for 24 hours, that is, the number of astrocytes was reduced, which indicated antiCD81 inhibited the proliferation of astrocytes and the effect showed a dosedependent pattern.2By cell cycle analysis, a progressive dosedependent decrease was found in the index of cells in G0/G1 phase and an increase in S phase. Such as, the index of cells in G0/G1 phase, was 82.73 in 0, is 8216 in 0.5mg/L, was 78.58 in 5mg/L. Conclusion AntiCD81 inhibits the proliferation of astrocytes and the number of astrocytes is reduced.