Membrane fatty acids in normal and experimentally induced diabetes mellitus in rats were investigated. This study was carried out on 120 male rats. The rats were divided into two equal groups of 60 rats each. Group Ι :(Control group):Injected with citrate buffer only. Group Π :( Diabetic group): Injected with a single intraperetinoel (i.p) injection of 50 mg/kg of streptozotocin for diabetes induction. Blood samples were collected in tubes containing trisodium citrate 3.8 % from all animal groups five times at 2, 4, 6, 8 and 10 weeks from the onset of diabetes induction. Plasma were separated and processed directly for glucose, total cholesterol, triacylglycerols, HDL–C, LDL-C, VLDL-C, NEFA, and L- malondialdehyde (L- MDA) determination. Moreover, total cholesterol, phospholipids and fatty acids composition in erythrocyte membrane were also analyzed. The obtained results revealed that, a significant increase in plasma glucose, total cholesterol, triacylglycerols, LDL-C, VLDL-C, NEFA, L-MDA and significant decrease in HDL-C concentrations were observed in streptozotocin-induced diabetic rats when compared with the non-diabetic control group. Also, a marked decrease in total cholesterol and Phospholipids concentrations were observed in erythrocyte membrane in streptozotocin-induced diabetic (STZ-D) rats. Moreover, fatty acid composition in erythrocytes of STZ-D rats revealed significant decrease in the percent of pentadecyclic and palmitic acids and increase in stearic and arachidic acids percent during different periods of diabetes. From the obtained results it could be concluded that, experimental diabetes mellitus extensively alters and induced disturbances in lipid metabolism in male rats. Also, Streptozotocin induced diabetes in rats alters erythrocyte membrane fatty acid composition.