Twelve-minute run test developed by Cooper in 1968 is a popular field test to evaluate an individual's cardiorespiratory fitness. However, the test requires high subject motivation and is accompanied by a high cardiovascular risk because of its maximal nature. In an attempt to avoid this flaw, this study sought to develop a 12-min submaximal run test and to validate it as a field test of cardiorespiratory fitness. Twenty-eight men, aged 19-34 years (22.3±3.6), served as subjects. Individual's cardiorespiratory fitness was evaluated by the distance covered in 12 minutes at the intensity corresponding to 13 on the Borg's ratings of perceived exertion (RPE13). All of the subjects performed a maximal stress test, the 12-min submaximal run test and the 12-min maximal run test. VO_<2max> and VO_<2AT> of the subjects averaged 57.9±7.5 ml/kg/min and 45.4±8.0 ml/kg/min, respectively. The distance covered in 12-min submaximal run test (2758±306 m) was significantly shorter than that covered in 12-min maximal run test (3105±394 m). Analyses of data indicated that aerobic capacity (VO_<2max> and VO_<2AT>) significantly correlated with the 12-min submaximal run (r=O.85 and O.86, respectively) and with the12-min maximal run (r=0.77and 0.81, respectively). Although the intensity of the 12-min submaximal run test was lower, their relationships were higher than that of the 12-min maximal run test. Our findings suggest that 12-min submaximal run test is a better cardiorespiratory fitness test than 12-min maximal run test. Furthermore, we attemped to develop equations to predict VO_<2max> and VO_<2AT> using the distance covered in 12-min submaximal run and age. Multipule regression analyses to predict VO_<2AT> and VO_<2max> yielded the following equations: the distance in the 12-min submaximal run (m) X_1 and age (yr) X_2. VO_<2max>=0.0021X_1(m) -0.52X_2(yr) +0.75 (R=0.89, SEE=3.81ml/kg/min) VO_<2AT>=0.0019X_1(m) -0.56X_2(yr) +17.93 (R=0.89, SEE=3.64 ml/kg/min) It was concluded that the distance covered during the 12-min submaximal run was a highly valid indicator of cardiorespiratory fitness.