The aim of the experiments was to investigate the effect of Fructus Tribuli on the blood pressure, plasma renin activity, plasma levels of aldosterone and atrial natriuretic peptide (ANP) in spontaneously hypertensive rats (SHR). The results of this study were as follows: 1. Systolic blood pressure decreased significantly after the administration of Fructus Tribuli water extract 0.03 ㎖/200 g. 2. Plasma renin activity and plasma levels of aldosterone were not changed after the administration of Fructus Tribuli water extracts. 3. Plasma levels of atrial natriuretic peptide (ANP) decreased significantly after the administration of Fructus Tribuli water extracts.