The aim of this study was to investigate the influence of attitudes towards mathematics and metacognitive awareness on mathematics achievement of high school students. In addition, this study interested in examining gender differences on mathematics achievement. The respondents of this study were 103 students of a senior high school in Tangerang, Indonesia. Attitudes Towards Mathematics Inventory (ATMI) was used to measure students’ attitudes towards mathematics, and Metacognitive Awareness Inventory (MAI) was used to measure metacognitive ability, whereas mathematics achievement was measured from the value obtained in the school report cards of the semester when the research was being conducted. The results revealed that attitudes towards mathematics and students’ mathematics achievement were significantly correlated (r = 0.505; p < 0.001). No significant correlations were shown between metacognitive skills and mathematics achievement (r = 0.081; p > 0.05), as well as between attitude towards mathematics and metacognitive skills (r = 0.143; p > 0.05). The regression model was fit in predicting the contribution of attitudes towards mathematics and metacognitive skills on mathematic achievement for 25.5%. However, looking at the p value of the t test it was shown that the attitude towards mathematics contributes to the model, but not the metacognitive skills. No significant difference was found on mathematics achievement.