Erythroleukemia disease is caused by over production of malignant blood and immature large number of blood cells enters into peripheral compartment. Biophysical and biochemical changes in plasma and erythrocyte membrane in erythroleukemia treated rats were identified. Our study, leukemia is experimentally exposed in rats were injecting erythroleukemia cells (FLC) (H-2d) intravenously in adult rats and normal control rats were maintained. Significant increase in the activity of blood glucose, proteins levels, aspartate transaminase (AST) and alanine transaminase (ALT) values and significant decrease in haemoglobin (Hb), albumin levels in erythroleukemia treated rats were observed when compared with control rats. Cholesterol and low density liproprotein (LDL) levels increased significantly in erythroleukemia treated rats but triglycerides, high density lipoprotein (HDL) and very low density lipoprotein (VLDL) levels decreased significantly. Levels of red cell membrane cholesterol decreased in erythroleukemia treated rats in comparison with control while levels of phospholipids and proteins increased in erythrocytes of erythroleukemia treated rats. Red blood cell (RBC) and white blood cell (WBC) counts increased significantly and platelet count decreased. C/P (cholesterol/phospholipid) ratio decreased significantly in erythroleukemia treated rats. This study has been undertaken for the first time to investigate the effect of (FLC) (H-2d) erythroleukemia cells (treated) in intravenously in adult rats and normal control rats. Results indicate biophysical and biochemical alterations at molecular level in plasma and erythrocyte membrane.