One of the factors that affect the success of reading comprehension ability is grammar mastery. Students who master grammar will have a better understanding of the text and will be able to comprehend it more quickly. In this case, this research aims to find out the correlation between grammar mastery and reading comprehension ability in third-semester students of the faculty of teacher training and education at University of Islam Malang. This research used a quantitative approach with a correlation design. The sample consisted of 29 English department students in the third semester of the faculty of teacher training and education at the University of Islam in Malang. The data was collected by using a score of grammar and reading. Then, the data were analyzed by applying Pearson Product Moment Correlation analysis. The research findings showed a significant positive correlation between grammar mastery and reading comprehension ability because the significance demonstrated on the table was 0.000<0.05 level of significance. Then, the coefficient correlation obtained shown on the table was 0.631. According to the significant interpretation, the correlation was in the range of 0.40-0.60, indicated a moderate correlation between those two variables. The result of the previous researches was similar with the present research. It was indicated that grammar mastery was significantly correlated with reading comprehension ability. Therefore, it was concluded that the students’ grammar mastery contributed significantly to their reading comprehension ability. Based on the finding above, it can be suggested that students should involve grammar when reading to get the message conveyed by the author. Besides that, the role of the lecturer is also essential to motivate students so that they can improve their grammar knowledge. Keyword: Correlation, Grammar Mastery, Reading Comprehension