This study is aimed to examine the impacts of aerobic exercises with different strenhrth levels on the changes in blood stress hormones and immunoglobulines (IgA, G & M) and identify the optimal exercise strength to help health enhancement and maximize the exercise effect. It is also aimed to provide the basic data for health enhancement for general public and athletes and to help athletic ability enhancement based on the findings regarding the optimal exercise strength and physical changes in the resting time. The subjects were 10 male students from I university located in Incheon, Korea. The exercise strengths in this study were VO₂max 20%, 40% and 60%. This study adopted a repeated measure experimental design. The blood samples were taken from cardinal veins 3 times: before-exercise, after-exercise and during resting time. The data was submitted to SPSS 12.0(SPSS Inc, Chicago, IL, USA) two-way repeated measure ANOVA. The significance level was set at α = .05. The cortisol concentration showed significant difference at VO₂max 60%. Catecholamine also showed significant difference at VO₂max 60%. The change rate showed considerably significant difference at VO₂max 60%. There was no significant difference in the changes of immunoglobulines (IgA, IgG, and IgM) at any strength level. Conclusively, these results indicate that combination of exercise at low strength level and rest may lead to the reduction of stress hormone excretion and the increased immunoglobuline level. In addition, it is required to develop a systematic exercise program for different ages, gender and vocations as well as to disseminate the exercises further sub-classified in their strengths for health enhancement. It is also required to conduct the research to propose the strength criteria for immunity enhancement.