Arsenic trioxide (ATO) has been established to be an effective agent for treating newly diagnosed and relapsed acute promyelocytic leukemia (APL) patients. Laboratory data suggest that ATO induces apoptosis of hematopoietic or several solid tumor cells. However, to date, its effect on lung carcinoma has not been fully explored. In the present study, we investigated the effect of ATO on human lung carcinoma PG cells in vitro. We found ATO significantly inhibited the proliferation of PG cells in a dose- and time-dependent manner. ATO-induced apoptosis of PG cells was confirmed by the observance of typical morphological changes and detected by the analysis of flow cytometry (FCM). ATO significantly inhibited Bcl-2 and Pgp expression of PG cells by SABC immunohistochemistry and FCM analysis. In conclusion, our findings indicated that ATO induced apoptosis of PG cells and down-regulation of Bcl-2 and Pgp expressions, and these data might provide some theoretical basis for its clinical use in treating lung carcinoma.