Abstract: Objective The present study was designed to determine the effects of IMD1-53, a member of Calcitonin-CGRP family, on arterial pressure in rats and its possible mechanism. methods Rat arterial pressure was measured after i. v. administration of IMD1-53 3.0 nmol/kg for 45 min. Nitrite concentrations were measured by Greiss method and NOS activation and L-Arg uptake were assayed by radio assay. Results IMD1-53 reduced arterial pressure which was more prominent than that by equipment adrenomedullin. Incubated vascular tissues with IMD1-53 resulted in a concentration-dependent increase in the nitrite content, eNOS activation and L-Arg uptake. As compared with controls, 10^-7mol/L IMD 1-53 increased nitrite（+59%）, eNOS activation（+356%）, and L-Arg uptake（+108%）. Conclusion This results suggest that IMD1-53 had substantial hypotensive effect on rat which may be mediated by NO/NOS pathway.