This study investigated the relationship between academic self-efficacy and psychological adjustment among 2821 students (grades 7 to 12) who were selected from all Omani school districts. It also aimed at exploring the predictive possibility of academic self-efficacy by psychological adjustment, and identifying the differences in academic self-efficacy and psychological adjustment according to gender and age. Two scales of academic self-efficacy and psychological adjustment were applied in order to obtain study data, after verifying their validity and reliability. The results showed statistically significant differences due to gender and class in both academic self-efficacy and psychological adjustment. Moreover, results of the multiple regression analysis showed that the adaptive adjustment subscale was the only significant predictor of academic self-efficacy and contributed with a percentage of (15.2%) in explaining the difference in students' scores in the academic self-efficacy scale.