Medicinal plants have been widely used in the complementary and alternative medicine. In addition to various bioactive organic substances, the efficacy of bioactive peptides released from the plant proteins by the digestive enzymes was become a research interest. In this study, crude protein extracts of ninety-four medicinal plants were subjected to hydrolysis by pepsin. Each plant hydrolysate was filtered through a 3kDa molecular weight cut-off membrane. The peptide mixture from each plant was then evaluated for cytotoxic effects against human gastric carcinoma (KATO-III, ATCC No.HTB103) cell line by MTT assay. Only the peptides from three medicinal plants includings rhizome of Gynura pseudochina var. hispida, stem bark of Streblus asper Lour and seed of Piper nigrum showed potent cytotoxicity against the cancerous cell line with no effect to African green monkey kidney cell line (Vero, ATCC No. CCL 81) at 100 ug protein/ml. The peptides from rhizome of Gynura pseudochina var. hispida showed the highest cytotoxicity with an IC50 value of 55.28 µg protein/ml. Isolation and identification of the peptide responsible the cytotoxic effect is on going.