Introduction: Physical activity causes changes in hematological parameters in athletes which finally result in cessation off their exercises, an issue that should be given attention. There is limited data avaliable about the effects of protein supplements, containing amino acids and other useful substances, on hematological parameters of resistance to exercise in athletes. This study was carried out to investigate the effect of whey protein supplementation, after resistance to exercise in healthy athletes. Material and Methods: In this clinical trial, changes of hematological parameters were studied after one month exercise training and whey protein supplementation in 32 healthy volunteers (16 treated cases 16 controls placeboes). Each day, whey protein supplement( 6.6 g/day) and placebo(same dose, starch) were consumed between meals, by with the volunteers. Every one exercised with 80% 1RM, basically on stationary circuit principal, for one hour a day, five days a week. Before and after beginning of study, fasting blood specimens were taken and WBC, RBC, HGB, HCT, MCV, MCH, MCHC, PLT and percent of white blood cells were measured separately. Statistical analyses were carried out using Student t- test and paired t-test (SPSS version 15). Results: Levels of WBC, RBC, HGB, HCT, PLT, MCHC in two groups significantly (P<0.05) decreased, but there was no difference between two groups. MCV increased in the groups, but again there was no difference between them. MCH and percent of lymphocytes were unchanged in both groups. In the supplement group, the percentages of the neutrophils and other white blood cells showed no significant changes, but in the placebo group, there were significantly increased and decreased, respectively. However there was no significant difference between the two groups in the percentage of white blood cells, separately. Conclusion: The present study showed that one month of Whey protein supplementation with 6.6 g/day is ineffective on hematological parameters changes after resistance to exercise. Further studies, with different dosages and longer periods of time are recommended.