Objective To explore the inhibition of juglone in Qinglongyi on A-549 cells in vitro.Methods MTT assay was used.Laser confocal scanning microscope was used to observe apoptotic morphology.Changes of cell cycle are studied by flow cytometry analysis.Results MTT assay showed that juglone had a marked growth inhibition in A-549 cells and the IC50 is respectively 3.4×10-5 mol·L-1,1.8×10-5 mol·L-1 and 2.6×10-6 mol·L-1 after treatment for 24,48 and 72 h by juglone.Through Laser confocal scanning microscope,we can see that juglone can induce the apoptosis.Cell cycle changes are analyzed by flow cytometry with cells at G1 phase significantly less than those of control and cells at G2 phase significantly more than those of control.Conclusions It suggests that juglone could apoptosis of A-549 cells with the cell cycle arrest on G2 phase in distinct dose-dependent manner. Objective To explore the inhibition of juglone in Qinglongyi on A-549 cells in vitro.Methods MTT assay was used.Laser confocal scanning microscope was used to observe apoptotic morphology.Changes of cell cycle are studied by flow cytometry analysis.Results MTT assay showed that Juglone had a marked growth inhibition in A-549 cells and the IC50 is respectively 3.4×10-5 mol·L-1, 1.8×10-5 mol·L-1 and 2.6×10-6 mol·L-1 after treatment For 24,48 and 72 h by juglone.Through Laser confocal scanning microscope,we can see that juglone can induce the apoptosis.Cell cycle changes are analyzed by flow cytometry with cells at G1 phase significantly less than those of control and cells at G2 phase Significantly more than those of control.Conclusions It suggests that juglone could apoptosis of A-549 cells with the cell cycle arrest on G2 phase in distinct dose-dependent manner.