Many studies acknowledge that English proficiency contributes to academic performance, eventually affecting one's career. This study, therefore, aimed to investigate whether English proficiency (EPT) could predict students' academic performance at a state Islamic university in Indonesia. A quantitative approach was used, in which the data of students' EPT and their Grade Point Averages (GPAs) were collected from 4,959 bachelor's degree seeking students from various faculties. These data were taken from the university's information center and then analyze using regression analysis to estimate if EPT significantly predicted GPA, whose finding was statistically significant (R2 = [0.016], F (1, 4958) = [82.885], p = [0.000]). Further regression analysis was carried out at the faculty level, and the finding indicated that EPT at the faculty of medicine contributed to academic performance the most (R2 = [0.362], F (1, 96) = [54.554], p = [0.000]). These findings mean that English proficiency can explain 1.6% of the variation in academic performance at the university level across faculties but much more with 36.2% at the faculty of medicine, implying the need to observe the learning process in each faculty to understand how English is used. In addition, it is also important to further study other factors affecting academic performance.