Background : Hypertension promotes progression of renal diseases, and causes cardiovascular diseases which are the important etiology of morbidity and mortality of chronic renal failure. So the appropriate treatment of hypertension is crucial in patients with renal diseases, and angiotensin-converting enzyme inhibitor is one of the most widely used. We evaluated the efficacy, side effects and influence on renal function of fosinopril sodium$(Monopril^{circledR})$, a relatively new angiotensin-converting enzyme inhibitor, in hypertensive patients with renal insufficiency. Methods : Patients with renal insufficiency and Hypertension were enrolled. They stopped other antihypertensive medications except ${eta}-blockers,$ and had 4 weeks of washout period with placebo administration At the start of the treatment period, fosinopril sodium$(Monopril^{circledR})$ was started long once daily, and 2 weeks later blood pressure response was evaluated. When the goal blood pressure was achieved$(reduction;{geq}20/10mmHg;than;before;treatment;or;absolute;value;{leq}140/90mmHg)$, the same dosage was given for another 4 weeks and study was terminated. If blood pressure reduction did not reach the goal, the dosage was increased to 20mg daily, and then 40mg daily. Results : Eighteen patients participated in thid study, of whom 10 were men and 8 women The age ranged from 28 to 64 years, and the median was 55 years. According to the JNC VI classification 3 were stage 1, 12 were stage 2, and 3 were stage 3. The blood pressure fell signicantly from $157.3{pm}13.2/100.6{pm}8.0mmHg(mean{pm}standard;deviation)$ to $144.6{pm}28.4/88.8{pm}11.3mmHg$ after treatment(p<0.05). When the patients were classified according to the blood pressure response, 9 were in reduction category(50.0%), 2 reducing tendency(11.1%), 6 no change(33.3%) and 1 increasing tendency(5.6% ). The dosages needed to achieve reduction or reducing tendency were 10mg in 5, 20mg in 1, and 40mg in 5. Pulse rate and body weight did not change after treatment. Laboratory tests including CBC, chemistry, blood and urine osmolality, creatinine clearance revealed no significant changes after treatment except serum calcium, phosphorus and potassium. Serum calcium and phosphorus levels decreased but the amounts were small so there was no clinical problem. Serum potassium level increased from 4.7 to 5.0mg/dl, and it did not seemed to impose a problem in medication Renal function measured by creatinine clearance showed no change. Side effects were observed in 6 patients. Five patients complained of cough, but the degree was not severe. Other complaints were nausea, vomiting, febrile sense, edema, rash and pruritus. The symptoms were observed in 1 or 2 patients, and the degrees were mild and they were transient in most cases None of the side effects became a reason to step the medication. Conclusion : Fosinopril sodium$(Monopril^{circledR})$ was an effective angiotensin-converting enzyme inhibitor in lowering blood pressure in hypertensive patients with renal insufficiency, and safe and tolerable without dosage modification.