Purpose: The purpose of this study was to explore the relation of self-efficacy with environmental factors, personality, and academic achievement in medical students. Methods: Study subjects consisted of 141 first-year medical students at Korea University Medical School during one academic year (2003～2004). All participants completed a 24-item questionnaire on self-efficacy beliefs, a 16-item questionnaire asking demographic and socioeconomic data, and the Temperament and Character Inventory (TCI). Spearman sorrelation of selfefficacy with other variables was generated. The differences of self-efficacy scores according to the level of satisfaction with school life, total family income per month and the reasons for entering medical college were analyzed by ANOVA. Results: Age and overall satisfaction with school correlated with self-confidence and total family income per month was related to self-regulation. Students who entered medical college due to the socioeconomic stability of medicine showed significantly lower preference for task difficulty than those who had other reasons for entering medical college. The GPAs of premedical studies correlated with self-regulation and the GPAs of Med 1 and the cumulative GPAs of premedical and Med I were related to the preference for task difficulty. Conclusion: This result supports that self-efficacy beliefs were related with some environmental factors, personality and academic achievements in medical students.