A series of peptidyl hydrazones was synthesized, and their inhibitory activity against mu-calpain and water-solubility were measured. Among these compounds, N,N-dimethyl glycyl hydrazone 6, which inhibited mu-calpain with IC(50) of 0.37 microM, possessed the appropriate water-solubility. Furthermore, hydrazone 6 was found to possess the excellent in vitro metabolic stability.