The purpose of this study was to investigate the correlation between students’ English proficiency (as measured by using standardized local test provided by the school) and their academic achievement in Science subjects (Biology, Chemistry, and Physics subject’s scores from the examination in the first semester and second semester of 2014-2015 academic year) in MAS Ruhul Islam Anak Bangsa (Islamic Boarding School). The data were collected from 33 bilingual students of third grade. In this research, both secondary data of students’ English proficiency and data of their academic achievement in Science subjects were used in order to answar the research questions. The documentation of the students’ English proficiency and their academic achievement in Science subjects were used as the instruments. To analyze the correlation between the variables, SPSS version 18 was used. The results revealed that students’ English language proficiency has significant positive correlation with their academic achievement in Biology, Chemistry, and Physics with r1=0.870; r2=0.917; r3=0.844 respectively. Based on these findings, it is recommended to give a special attantion to bilingual students to develop their English proficiency in order to increase their academic achievement.