Classical methods for the regulation of exercise intensity, based on objective physiological indices, e.g.heart rate oxygen uptake, have been indicated to be inadequate for maintaining subjective motivation contributing to exercise adherence. Rating of perceived exertion (RPE) developed by Borg has also been utilized in the setting of exercise prescription. However, a number of problems with this approach have been pointed out by some investigators. Therefore, we have proposed another method for self-prescription of exercise intensity through evaluation of psychological and physiological validity. The purpose of this study was to compare cardiorespiratory and psychological responses at self-prescribed power outputs 20-min cycling before (Pre) and after (Post) a 3-month supervised aerobic exercise program. Fourteen healthy middle-aged women (mean age 46±5 years) who had not taken regular exercise during the previous 5 years volunteered to participate in the study. Although the percentage lactate threshold (%VO_2LT) during the 20 min of cycling at Pre (108%VO_2LT) was significantly higher than that at Post (98%VO_2LT), the intensities selected by the subjects at Pre were also considered safe and effective. Furthermore, the subjects reported comfortable experiences and improvement of mood, which were recognized to have positive effects on exercise adherence, after 20-min cycling under both conditions. Thus, it is suggested that use of self-prescribed intensity for exercise prescription can be one of the ways of solving problems related to execise adherence.