In this study the effect of water extract of Sophora tonkinensis Gapnep (RST) was investigated on the growth of human lung carcinoma A549 cells. Exposure of A549 cells to RST resulted in the growth inhibition in a dose-dependent manner as measured by MTT assay. The antiproliferative effect by RST treatment in A549 cells was associated with morphological changes such as membrane shrinking and cell rounding up. RST treatment did not induce the cell cycle arrest and the levels of tumor suppressor p53 as well as cyclin-dependent kinase inhibitor p21(WAF1/CIP1). It was found that RST treatment decreased the levels of cyclooxygenase (COX) -2 mRNA and protein expression without significant changes in the expression of COX-1 and inducible nitric oxide synthase (iNOS), which was correlated with a decrease in prostaglandin E2 (PGE2) synthesis. RST treatment also slightly inhibited the levels of human telomerase reverse transcriptase (hTERT) mRNA and protein expression, and the activity of telomerase. Taken together, these findings suggested that RST-induced inhibition of human lung carcinoma A549 cell growth was aoosciated with the inhibition of COX-2 expression and PGE2 production. These results provided important new insights into the possible molecular mechanisms of the anti-cancer activity of RST.