Rehmannia Radix is a thick tuberous root about 3-6 cm diameter. The tuberous root is repared for medicine. The material in the fresh state is shengdihuang (生地黃). The material in the dried state is gandihuang (乾地黃). Shudihuang (熱地黃) is made by taking juicy roots, washing them in millet wine, steaming on a willow frame in a percelain vessel, drying, and resteaming and redrying nine times. The aim of this experiments was to investigate the effect of Rehmannia Radix Water extracts on the plasma renin activity and plasma levels of aldosterone and atrial natriuretic peptide (ANP) in rats. The results of study were as follows: Plasma renin activity was not changed after administration of Rehmannia Radix water extracts. Plasma levels of aldosterone was decreased significantly after administration of Shudihuang (熱地黃) water extracts. Plasma levels of atrial natriuretic peptide was increased significantly after administration of Shudihuang (熱地黃) water extracts.