Impaired red blood cell deformability is a hemorheological perturbation induced by many kinds of diseases. An increase in free radicals causes a reduction in erythrocyte flexibility and deformability. Carnosine is a dipeptide abundant in skeletal muscle and brain of humans. One of the main function of carnosine is its antioxidant and free-radical scavenger effect. In this study our aim is to investigate the protective effect of L-carnosine on RBCs in H(2)O(2)-induced oxidative stress in vitro conditions. Twenty male wistar albino rats, 10 were 3 months old, 10 were 12 months old used. The blood from each rat were divided into ten tubes and these blood samples divided into two groups. The first tube of the first group was the control and the rest 4 tubes were treated with different concentrations of L-carnosine. All tubes in the second group were incubated with H(2)O(2) additively. The deformability indexes of the erythrocytes were measured by a laser diffractometer (Myrenne Rheodyne SSD).L-carnosine has improved the RBC deformability significantly which is impaired by H(2)O(2) treatment (p<0.05). Increase in deformability is more significant in young rat group when compared to old rat group.L-carnosine, as an antioxidant molecules, has a dose dependent positive effect on RBC deformability and has improved or protect the deformability of erythrocytes, especially in young rat group which impaired by H(2)O(2)-induced oxidative stress in vitro conditions. The results of this study first suggest that L-carnosine supplemention can be used to improve the RBC quality or to protect them from oxidative damage in survival of RBC in the circulation.