Aim: Microalbuminuria is typically observed in renal transplant recipients with systemic hypertension. The effects of angiotensin II type I receptor antagonist (losartan) on the hypertensive recipients have been evaluated. However, the clinical background of normotensive recipients with microalbuminuria and the effect of losartan administration in those subjects have not been clarified. One of the two purposes for the present study was to investigate the clinical characteristics of normotensive recipients with microalbuminuria. The other was to evaluate the effect of losartan on urinary excretion of albumin in these patients. Methods: The clinical data and the change of the single kidney glomerular filtration rate (GFR) for the graft by radionuclide study were assessed in 13 normotensive recipients with microalbuminuria. These were compared with the data of 13 normotensive patients without microalbuminuria. The 13 recipients with microalbuminuria were treated with losartan for one year and urine excretion of albumin, N-acetyl-β-D- glucosaminidase (NAG) and serum creatinine (S-Cr) levels were measured. Results: The GFR of the grafts from donors to recipients significantly increased (30.9 to 55.2 mL/min) in microalbuminuric recipients, but did not significantly increase in the non-microalbuminuric recipients. Decreases of the urinary excretion rate of albumin (351 ± 261 at baseline to 158 ± 14 mg/gCr at 12 months), NAG (13 ± 5 to 10 ± 3 IU/gCr) and S-Cr (1.7 ± 0.6 to 1.5 ± 0.4 mg/dL) were observed in the microalbuminuric recipients with losartan administration. Conclusions: The present study suggests that an increased single kidney GFR of the graft from the donor in situ to the recipient might be a cause of microalbuminuria in normotensive recipients. The one-year effects of losartan were observed in terms of the decrease in urinary excretion of albumin, NAG and S-Cr levels.