A study of albuminuria, creatinine clearance (CCr) and blood pressure of streptozotocin (STZ)-induced diabetic rats with or without treatment by a prostacyclin (PGI<sub>2</sub>) analog, beraprost sodium (BPS), is described. Glomerular prostanoid synthesis was measured by gas chromatography (GC) mass spectrometry. Renal specimens stained with hematoxylin and eosin and periodic acid-Schiff were examined by light microscopy. Mean values of albuminuria in BPS-treated diabetic rats were significantly decreased compared with those in nontreated diabetic rats. The ratio of kidney to body weight in the BPS-treated diabetic rats was significantly lower than that in the nontreated diabetic rats. Levels of CCr and blood pressure were decreased in diabetic rats after the treatment with BPS. GC mass spectrometry showed that BPS did not influence the glomerular synthesis of PGI2 and TXB2. No histologic injury in the renal tissues was observed in the diabetic rats with or without BPS treatment. We concluded that BPS (PGI<sub>2</sub> analog) might decrease the levels of urinary albumin excretion and CCr due to its vasodilating effects in the early phase of STZ-induced diabetes in rats.