Objective:To le the effect of allitridi on inducing mitotic arrest in human gastric cell line SGC-7901 and its possible mechanisms.Methods:We treated SGC-7901 cells with ailitridi,and observed the proliferation inhibitory rate with MTT colometric assay,changes of cell cycle using flow cytometry and Switzerland-Giemsa’s staining,and morphologic changes of the microtubule structure and location changes of cyclin B1 expression using immunofluorescence and confocal laser scanning microscope.Furthermore,the expression of cyclin B1 was analyzed quantitatively using Leica confocal software.Results:SGC-7901 cells were inhibited after exposure tO allitridi and the IC50 was 7.2μg/ml for 24 h,20μg/ml for 72 h.When the cells were treated with allitridi at concentrations of 3,6,and 9μg/ml for 24 h respectively,there was a declining tendency in the percentage of G0/G1 cell but an increasing tendency in G2/M cell in the allitridi treated group compared with that of control (P＜0.01).When cells were treated allitridi at concentration of 6 μg/ml for 24 h,its mitotic index was much higher(P＜0.01) than that of control,suggesting that allitridi caused arrest of gastric cancer cells in M phase.The cells were treated with allitridi became more shrunken and nepheioid,in which the microtubule networks disappeared,while the control cell exhibited an intact microtubule network.Contrasting with normal existence mainly in the cytoplasm,the cyclin B1 was expressed more significantly and concentrated in the nucleus after exposure tO allitridi.Fluorescence intensity of cyclin B1 protein in cells treated with allitridi was much more higher than that of control(P＜0.001).Conclusion:Allitridi can induce arrest of SGC-7901 cells in M phase,probably through enhancing microtubule depolymerization by elevating the expression of cyclin B1.