The adhesion molecule integrin α3β1 is the major receptor of podocyte to the glomerular capillary basement membrane (GBM). Since progressive alteration of the glomerular extracellular matrix (ECM) compartment leading to GBM thickening is common in diabetic nephropathy, we investigated the cellular distribution of α3β1 integrin in podocytes of patients with diabetic nephropathy and streptozotocin-induced diabetic rats, and we evaluated the effects of high glucose on the cultured rat podocytes. Both human and rat kidneys were stained using the immunoelectron microscopy and immunoperoxidase technique with mouse monoclonal antibodies to human integrin α3 subunit. The results showed that both the number of immunogold particles and the staining of integrin α3 subunit on podocytes were weaker in patients with diabetic nephropathy than those of control kidneys. The staining of α3 on podocytes in the poorly-controlled diabetic rats was also weaker after one and three months of hyperglycemia. However, the staining was identical to controls in rats with only one week of hyperglycemia. High glucose (25 mM) but not streptozotocin in vitro suppressed the α3 expression of cultured rat podocytes. Our results demonstrated that the expression of integrin α3β1 on podocytes was suppressed in both human and rats with diabetes, possibly due to the effects of hyperglycemia, and the suppression became more severe with the duration of diabetes.