【Abstract】 Objective: To investigate the inhibition effect of Brucea javanica oil self microemulsion on the p roliferation of human lung cancer cells. Methods: The human lung cancer cells A549 were cultivated with Brucea javanica oil self microemulsion . The effects of Brucea javanica oil self microemulsion on the proliferation of A549 cells were observed using MTT method and flow cytometry. Results: Brucea javanica oil self microemulsion could inhibit the growth of A549 cells in dose-dependent and time-dependentmanner . The cell cycle analysis showed that the percentage of G0 /G1 phase cells increased and S phase cells decreased. There was significant deviation (P<0.01) in interclass of the concentration of Brucea javanica oil emulsion 0.05mg/ml and 0.1mg/ml (P<0.01). The percentage of G2 / M phase cells decreased. Conclusion: Brucea javanica oil Self microemulsion could inhibit the proliferation of A549 cells in vitro and the mechanism may relate to its preventing the cell cycle in G0 /G1 phase.