Background : Due to increased interest in herbal medicines is recent years, medical circles have made studies of toxicity and side effects of herbal medicines. Particularly the kidney is sensitive to toxicity. A few reports concerning the side effects and toxicity of herbal medicine have been presented recently. This has bought on some distrust in herbal medicines among patients and western doctors. Objectives : The purpose of this study is to determine what effects long-term prescription of one herbal medicine may have on renal function. Methods : Nineteen patients took herbal medicine for eight weeks. Tests of their Blood Urea Nitrogen(BUN), Creatinine of blood plasma, and urine (chemical and microscopic) were taken before taking medicine and at the 2nd, 4th, 8th weeks. Results : After taking a herbal medicine, BUN and Creatinine decreased significantly or remained the same in comparison with the prior interval. Chemical and microscopic examination of urine showed no changes. Conclusions : The results suggest that taking this herbal medicine for a long time does not induce nephrotixicity. Further study is needed for investigating safety and toxicity of herbal medicines.