The objective of this study was to develop a new small molecular peptide, tyrosyl-seryl-leucine (tyroserleutide, YSL), as an anticancer drug. Our study investigated the effects of YSL on human hepatocellular carcinoma and cyclin, and explored its antitumor mechanism in vitro. In-vitro effects of YSL on human hepatocarcinoma cell BEL-7402 were assayed by the MTS (dimethylthiazol-carboxymethoxyphenyl-sulfophenyl - tetrazolium inner salt) method. The ultrastructure of tumor cells was observed by electron microscopy. DNA ladder was used to investigate apoptosis of BEL-7402 cells. The effects of YSL on the cell cycle of BEL-7402 cells were determined by flow cytometry. Expression of PCNA, P21, and P27 were investigated by real-time PCR and western blot in BEL-7402 cells. YSL inhibited the proliferation of BEL-7402 cells in vitro, induced DNA fragmentation, and changed their ultrastructure evidently, resulting in the necrosis and apoptosis of tumor cells. YSL interrupted cell cycle of tumor cells at G0/G1 and postponed their proceedings. YSL markedly enhanced the mRNA and protein expression of P21 and P27, and decreased the expression of PCNA of tumor cells. In conclusion, YSL significantly inhibited the growth of human hepatocellular carcinoma BEL-7402 cells and its anti-tumor effects may result from the upregulation of cyclin P21 and P27, and downregulation of cyclin PCNA.