The effects of Equiseti Herba Water-heating extract on the kidey & liver of rats were studied in 25 male Sprague-Dawley rats evenly divided into five groups, i.e., 5 rats each. The group I, which served as control and the group II, III, IV, were fed 300 mg/kg, 1000 mg/kg of Eqiseti Herba water-heating extract daily for one week, respectively. The group V was fed 1000 mg/kg of Equiseti Herba extract daily for two weeks. The effect of Equiseti Herba on the kidney and liver were determined by the measurements of the serum levels of BUN, creatinine, calcium, phosporus, sodium and potassium, total protein, albumin, transaminase (GOT & GPT) and cholesterol and 24hrs urine volume and GFR(ml/min), as well as by light microscopic and ultrastructural examinations of kidney and light microscopic examinations of liver in rats. The results were as follows; The groups II, III, IV were slightly higher than the control group on serum creatinine and potassium levels, but the group V was declined on serum creatinine and potassium levels, and 24hrs urine volume in spite of increased GFR. Histologically there was no remarkable changes in groups compared with the group I, except mild vacuolization of proximal convoluted tubule in group IV and V. These results suggested that equiseti Herba water-heating extract in rats induced reversible tubular changes on the kidney of rats. But the groups administrated by Equiseti Herba water-heating extract were not significantly higher than the control group on liver function test. Histologically there was no remarkable changes in groups II, III, IV & V compared with the group I.