Objective: To explore the effect of ligustri-astragali casein co-peptid(LACP) on human lung adenocarcinoma A549 cell differentiation and the related mechanism. Method : MTT assay for human lung adenocarcinoma A549 cells; containing 5%, 10%, 15%, 20% concentration of LACP serum was used. The influence of LACP containing serum on differentiation was evaluated by investigation of cellular nuclear-mass ratio and telomerase activity. Immunocytochemical method was used to observe the effect of LACP drug serum on the A549 Bax/bcl-2 expression. Results : The four kinds of different concentrations of LACP serum inhibited A549 cell proliferation. Among them, 20% of LACP showed the highest inhibitory rate; and reduced the cells nuclear -mass ratio. LACP serum promoted A549 cell bax/ bcl-2 gene expression for apoptosis, and compared with the serum-free control group, the difference was significant ( P <0.05). Conclusion : LACP containing serum has certain inhibitory effect on human lung adenocarcinoma A549 cells. LACP complex shows promotion to human lung cancer cell A549 differentiation. The mechanism may be linked to inhibition of telomerase activity. The complex induced apoptosis of A549 cells may be related to promotion of bax/bcl-2 gene expression.