Tyroserleutide (YSL) is a tripeptide treatment being developed by Shenzhen Kangzhe Pharmaceutical Co Ltd, a subsidary of China Medical System Holdings (CMS), for the treatment of liver cancer. It is initially separated and purified from the hydrolyzates of pig’s spleen, but now can be obtained by chemical synthesis, its chemical name is L-tyrosine-L-serine-L-leucine. Tyroserleutide is an active, low-molecular-weight polypeptide, comprised of three amino acids, that has shown antitumor effects on human hepatocarcinoma BEL-7402 in vitro and in vivo. Tyroserleutide has various advantages over the other bioactive peptides such as its low molecular weight, simple construction, nonimmunogenicity, specificity, few side effects, and ease of synthesis. Tyroserleutide is in Phase-III clinical trials for the treatment of liver cancer.