Objectives : The aim of the study was to evaluate the effect of WS on HepG2 cell cycle and expression of related genes. Methods : The MTT assay, Cell counting analysis, $[^3H]-Thymidine$ Incorporation Assay, Flow cytometric analysis, Quantitative RT-PCR were studied. Results : WS inhibited HepG2 cell proliferation in low concentration$(1-10;{mu]g/ml)$ which did not cause direct cytotoxicity, with dose-dependant manner. WS in-hibited DNA synthesis as well. Flow cytometric analysis on the HepG2 cell showed G2/M phase arrest. Conclusion : These results suggest that WS inhibits HepG2 cell proliferation not by the gene regulation but by G2/M phase arrest in the cell cycle. Thus further studies on the effect of WS in G2/M phase regulation are thought to be needed.