N-ω-chloroacetyl-L-ornithine (NCAO) serves as a powerful reversible competitive inhibitor of ornithine decarboxylase (ODC), displaying cytotoxic and antiproliferative properties against various tumor cell lines, with EC50 values spanning from 1 to 50.6 µM. In vitro studies reveal that NCAO promotes Apoptosis and restricts tumor cell migration. Additionally, it demonstrates significant antitumor efficacy in a mouse model, targeting both solid and ascitic tumors using the myeloma (Ag8) cell line. NCAO holds promise in the development of antitumor agents.