Since the HT29 cell line (ATCC Number: HTB-38) is isolated from a primary tumor of human colon tissue and is known as characteristic model of human colon cancer cells which produce carcinoembryonic antigen (CEA) and form well-differentiated adenocarcinoma consistent with colonic primary, grade I, in the present study, we investigated possible apoptotic and anti proliferative effects of genistein on HT29 colon cancer cells via the determination of caspase-3 and p38 MAPK gene expression level and their corresponding protein concentration. The gene discussed is CASP3; the disease is neoplasm.