We investigated the effects of Insamsapye-tang (ISSPT) water extract on the growth of human lung carcinoma A549 cells. Upon treatment with ISSPT extract, a concentration-dependent inhibition of cell viability was observed and cells developed many of the hallmark features of apoptosis, including condensation of chromatin. Flow cytometry analysis confirmed that ISSPT treatment increased populations of apoptotic-sub G1 phase. In addition, proteolytic degradation of poly(ADP-ribose) polymerase (PARP) and β-catenin protein were observed after treatment of ISSPT extract. These apoptotic effects of ISSPT in A549 cells were associated with marked inhibition of Bel-xL expression in a dose-dependent manner, however the levels of Bcl-2 and Bax expression were not affected. ISSPT treatment also induced the expression of tumor suppressor p53 mRNA and inhibited the expression of caspase-3 mRNA. The previous and present results indicated that ISSPT-induced inhibition of lung cancer cell proliferation is associated with the blockage of G1/S progression and the induction of apoptosis.