Using Malaysia TIMSS 2015 data, this study examined the association between eighth grade students' science achievement and mathematics score and the determining factors of science achievement. A total of 9,726 students participated in TIMSS 2015 with an average score of 508.60 with standard deviation of 89.86 for science and 501.57 with standard deviation of 86.46 for mathematics. Correlation coefficient between composite science and mathematics score is 0.88. The result of the multiple regression analysis showed that being a male, always speaking the language of test at home, having educated parents, students liking and valuing science and mathematics scores had a significant positive effect on science achievement. In contrast, having access to an internet connection and having confidence in science were found to have a negative influence on science achievement.