Vascular changes, the angioarchitecture of renal glomerular fine vessels in early diabetic KK-A^y mice of 4 months of age were examined by scanning electron microscopy of corrosion casts. Histologically, enlargement of glomeruli and dilation of glomerular capillaries were found. In resin cast specimens, glomeruli with diabetes were larger than normal, and an increase in diameter of the glomerular vessels was found in diabetic mice. No capillary proliferation, distortion of glomerular vessels and destruction of glomerular capillary loops were found in diabetic mice. The increased vascular diameter may explain the increase in blood flow in the glomeruli, affecting kidney function in early diabetes.