Abstract: Objective To investigate the effect of endostar on human lung cancer line A549 and the action machanism. Methods A549 cells were treated with endostar. The cell cycle was detected by flow cytometry(FCM)，and the expression of HIF-1 by enzyme linked immunosorbent assay(ELISA). Results Endostar could arrest A549 cells in G₂~M and S phases, and inhibit the expression of HIF-1 with the inhibition rate being increased with the time. Conclusion Endostar can increase the proportion of A549 cells in G2/M and S phases, which provides the basis for the inhibition of A549 cell proliferation.HIF-1 is an important factor in resistantce of chemotherapy and radiotherapy. Endostar can inhibit the production of HIF-1 in tumor cells, so combined used of endostatin maybe improve the curative effects of radiotherapy and chemotherapy.