"The purpose of this study was to evaluate the reliability of the Korean national fitness assessment using the O2run™ measurement equipment. The subjects for this study consisted of 416 adult males and females(age 20~60) selected randomly among those who underwent a medical examination and physical fitness test(strength, endurance strength, flexibility) at D university Lab. of science of physical fitness for measurement in Gyeonggi- do. A simple reliability analysis(sex, age) was used for research of the Korean national fitness assessment and O2run™ measurement equipment. The results were summarized as the following; it was found that both males and females in their 20's, 30's,40's and 50's showed high levels of reliability based on the Z-score calculated from a simple correlation analysis of muscular strength, muscular endurance, and flexibility assessed by the Korean national fitness assessment and O2run™ measurement equipment. Therefore it can be concluded that when targeting a large group of subjects, research for Korean national fitness assessment and establishing a respective baseline proved to be difficult and will require further research. Although it is also difficult to establish an alternative baseline for assessment required for further research, it can be said that further discussion is needed in order to develop a smallest baseline(or relative baseline) based on the physical characteristics, goals, and needs of the subjects. Key words : Korean national fitness assessment"