OBJECTIVES: To predict students' academic achievement (GPA) by Self-efficacy (SE). SE is defined as the self-perception that one can master a certain task or perform adequately in a given situation. METHODS: A descriptive cross-sectional survey was employed for studying the relationship between Self-efficacy and academic achievement (GPA) of all (178) 5th year pharmacy students at The College of Pharmacy, Chulalongkorn University, Bangkok, Thailand during the period of August to September, 2003. RESULTS: The final return rate of questionnaire was 171 (96.06%). The respondents average age was 22.02 years. Most (124) were female (72.51%). The reliability coefficient (Cronbach’s alpha) of Self-Efficacy (SE) scale was 0.87. The findings showed that there was positive relationship between SE and academic achievement (GPA) r=0.38 (p=0.03). The length of time for preparing for an examination by a female was longer than for a male (p=0.03). There was no difference between male and female SE (p=0.07). However, female’s GPA was significantly higher than male's (p=0.02). SE of the Bangkoker students was not different form the Non-Bangkoker students (p=0.87). Students who participated in activities had higher SE than students who did not (p=0.24) but the GPA of the two groups was not different (p=0.59). Attitude toward pharmacy profession had no impact on SE nor GPA (p=0.78, 0.82). The three predictors of the model were SE, Gender, and Time (to prepare the examination) R square=0.40, beta=0.38, 0.10, and 0.07 (p=0.02). IQ was not controlled in this study. CONCLUSIONS: Self-Efficacy was a good predictor of academic achievement of Chulalongkorn University, pharmacy student class of 2003.