Ectopic adipose tissue in skeletal muscle is implicated in the development of insulin resistance, which is frequently induced by abnormal dietary habits such as excessive eating and a high-fat diet. However, the characteristics of ectopic adipocytes are unknown. In this study, we investigated the characteristics of ectopic adipocytes in the skeletal muscle of spontaneously hypertensive corpulent congenic (SHR/NDmc-cp) rats as a model of insulin resistance from excessive eating. SHR/NDmc-cp rats displayed overt insulin resistance with high plasma glucose, insulin, and triacylglycerol concentrations relative to control Wistar-Kyoto (WKY) rats. In contrast, streptozotocin (STZ)-treated WKY rats had high glucose but low insulin concentrations. Ectopic adipocytes were found around blood vessels in the gastrocnemius in SHR/NDmc-cp rats. Areas of perivascular adipocytes and protein expression of resistin were greater in SHR/NDmc-cp rats than in control and STZ-treated WKY rats. The level of the phosphorylated (active) form of endothelial nitric oxide synthase in the gastrocnemius was lower in SHR/NDmc-cp rats than in the other groups. Insulin-resistant SHR/NDmc-cp rats showed enlarged perivascular adipocytes and greater endothelial cell dysfunction in the gastrocnemius.