Abstract: ABSTRACT Objective To study inhibition effects of methotrexate（MTX） enantiomers in human lung cancer A549 cells. Methods The cell morphological changes were observed by inverted phase contrast microscope. Cells growth inhibition was determined by MTT method .The cell cycle phases and apoptosis rates were analyzed by flow cytometry . Results Inverted phase contrast microscope observation cell morphogenesis changes after joining MTX enantiomers. The inhibition effects of of methotrexate enantiomers showed dose and time dependent inhibition in human A549 cells，the inhibition effect of L - (+) -MTX is stronger than the D - (-) - MTX. There were obvious interference effect on cell cycle and apoptosis of A549 cells by MTX enantiomers drugs treatment. Conclusion MTX enantiomers have an obvious chiral selective effect in human A549 cells, the inhibition effect of L - (+) -MTX is stronger than the D - (-) - MTX. Key words：methotrexate，Enantiomers, A549 cell line，proliferation，apoptosis

Key words: Key words：methotrexate, Enantiomers, A549 cell line, proliferation, apoptosis