Background: Chronic kidney disease (CKD) is a comprehensive disease concept that includes chronic glomerulonephritis such as IgA nephropathy or lupus nephritis, diabetic nephropathy and hypertensive nephrosclerosis. CKD is a risk factor for end stage kidney disease (ESKD) and cardiovascular diseases (CVD). It is considered that angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs) induce a marked renoprotective effect in patients with CKD. The purpose of the present Japan-Indonesia collaborative study was to evaluate the antiproteinuric effect of imidapril, one of the ACEIs, in hypertensive patients with CKD. Methods: Twenty three hypertensive CKD patients were treated with imidapril and a calcium channel blocker (CCB). Imidapril was added for patients who had been treated with a CCB such as diltiazem at the start of this study. When blood pressure (BP) did not reach the target level (<130/85 mmHg), imidapril dosage was increased to 10 mg/day and administered for 12 months. Alternatively, patients were treated with 5-10 mg/day of imidapril. Results: In the imidapril + CCB combination therapy, systolic blood pressure (SBP) and diastolic blood pressure (DBP) were significantly reduced, both at 6 months and at the end of the clinical study. Only DBP reached values below the target level. Urinary albumin excretion (UAE) levels were markedly decreased at 6 and 12 months when compared with the baseline values (0.45 ± 0.54g/g·Cr indicating typical overt proteinuria) and these decreases at both time points were significant. The UAE levels at both 6 and 12 months complied with the diagnostic criteria for microalbuminuria (< 0.299 g/g·Cr). Conclusion: In this collaborative study, a combination of imidapril and a CCB, such as diltiazem, significantly reduced BP, and reduced UAE, suggesting strict BP control may induce an efficient decrease in UAE. It appears that imidapril-based therapy has renoprotective effects in hypertensive patients with CKD.