Although studies have shown that an imbalance between effort and reward in the workplace negatively affects an individual’s physiological and mental health, few have looked at how this imbalance may affect the mental state of athletes. Therefore, this study aimed to evaluate the importance of the effort-reward imbalance (ERI) in athletes by examining whether psychological variables would differ depending on the ERI. To accomplish this, 795 registered collegiate athletes were recruited. Of them, 227 and 230 responses with the ERI in the bottom and in the top 30% of the ERI scale were selected to compare groups with a high and a low ERI. Athletes completed a self-reported 64-item questionnaire (general characteristics: 5; effort: 14; rewards: 14; grit: 12; burnout: 15; and continuous exercise intention: 4 items). Data analysis included reliability and validity using the Jamovi and SPSS/AMOS software. The results showed no significant differences in effort, reward, grit, burnout, and intention to continue to exercise based on gender, weekly training frequency, and hours of training per day. There were differences in effort, reward, grit, burnout, and intention to continue exercising based on the presence of a professional league. Additionally, differences were found in effort, reward, grit, burnout, and intention to continue exercising between the low and high ERI groups. There was a clear difference between the mental state of those who were satisfied with their effort and reward, and those who were not. However, given that the two groups spent approximately the same amount of time exercising each week, the difference may have been more a function of the psychology of athletes than an actual difference in effort and reward. As our findings confirmed that the level of the ERI in athletes is related to their mental state, further research is necessary to identify and control factors that affect the ERI in athletes.