The purpose of this study was to investigate the effects of age on the responses of hematologicalvariables to a single session of endurance exercise. For this reason 30 young (20-30 years); 30middle-aged (40-50 years) and 27 old (60-70 years) male subjects participated in the study.After determination of VO2Max; all subjects performed one session of endurance exerciseincluding 30 minutes cycling at 60-65% of VO2Max; which was followed by 30 minutes ofrecovery. In addition to measuring the hemodynamic variables; three blood samples were takenbefore; immediately after exercise and after 30 minutes of recovery and were analyzed forhematocrit; hemoglobin; red blood cell count; mean cell volume (MCV); mean cell hemoglobin(MCH); mean cell hemoglobin concentration (MCHC); white blood cell count; platelet count.Changes in response to exercise as well as recovery were compared among the three groups byusing independent one-way ANOVA. Endurance exercise resulted in significant increases(P<0.05) in all parameters except for MCV. Hemoglobin; hematocrit; red blood cell countincreased significantly in response endurance exercise by 7; 6 and 5.7 %; respectively; while allparameters except for MCV; MCH and MCHC during recovery were significantly (P<0.05)decreased. Hemoglobin and hematocrit during recovery were significantly decreased by 5.5 and5.2 %; respectively. There were no significant differences (P>0.05) among the responses of allparameters to endurance exercise and recovery in three groups. Based on the findings of presentstudy; it could be concluded that responses of hematological variables to acute enduranceexercise and recovery are not affected by age.