Abstract: m-Nifedipine (m-nif) is a new vasodilatory calcium antagonist with pronounced hypotensive action. A comparative study on the antihypertensive effects of m-nif, nifedipine (nif) and nitrendipine (nitr) in consciou rats, rabbits and renal hypertensive rats were carried out. Systolic blood pressure of rats was measured on the tail. The systolic and diastolic blood pressure of rabbits were measured directly from the common carotid artery. The hypotensive effects of m-nif, nil and nitr (rats 10 mg/kg; rabbits 8 mg/kg po) were studied on both animals. Peak effect was observed 4 h after oral administration in rats and 1 h in rabbits. The effects declined between 6-8 h after treatment in rats and 4～8 h in rabbits. The blood pressure returned to their initial values 24 h after administration. A quantitative comparison between the maximal % (4 h after medication) reduction of blood pressure was made by regression analysis. The E₅₀ values of m-nil, nil and nitr were found to be 33.7±3.4, 45.58±3.6 and 51.2±4.1mg/kg (90±9, 132±10, 142±11 μmol/kg) respectively. In renal hypertensive rats, m-nif, nil and nitr at the same dose of 10 mg/kg po significantly reduced blood pressure 4 h after administration.