Objectives: The aim of the present study was to predict students’ academic performance based on attachment styles and different levels of adjustment. Method: This is a correlational study. Samples included 383 students (167 girls and 216 boys) who were chosen using multi-stage cluster sampling from high school students of district 2 in Tehran; they completed Collins and Read’s Revised Adult Attachment Scale (RAAS) and Singha and Sing’s Adjustment Inventory for high School Students (AISS). Students' grade-point averages were used to measure their academic performance. Data were analyzed using Pearson’s correlation and analysis of regression. Results:  The results revealed a significant negative correlation between avoidant and anxiety attachment styles with academic performance (p<0.05; r=-0.43, r=-0.56, respectively), and significant positive correlation (p<0.05, r=0.56) between safe attachment style and academic performance. Also, academic, emotional and social adjustment had a significant relationship with students’ academic performance (r=0.66, r=0.67, r=0.71, respectively; p<0.05). About 62% variance of academic performance was predictable by attachment and adjustment styles. Conclusion: Considering the results of the current study, the importance of attachment styles and different levels of adjustment should be considered as important factory in academic achievement of students.