In this study, it was aimed to determine the relationship between primary school 4th grade students' reading comprehension level and mathematics course success. The study group of the research consists of 80 students selected by purposive sampling method, studying in the 4th grade of official institutions in the Pazar district of Tokat province. The research was prepared using the relational survey model in the perspective of quantitative research methods. The research data were obtained through the Reading Comprehension Level Determination Test and the Mathematics Achievement Test. SPSS program was used in the analysis of the data obtained as a result of the research, Pearson Product-Moment Correlation Coefficient was used to determine the relationship between reading comprehension and mathematics achievement, and unrelated sample t-test was calculated to determine the significance between students' reading comprehension level and mathematics course success according to gender variable. In this context, in the study, a positive and significant high-level relationship was found between the reading comprehension level of 4th grade students and their success in mathematics courses. According to the gender variable, a significant difference was found in favor of female students when both the reading comprehension levels and mathematics course achievements of the students were compared. Keywords : Reading, reading comprehension, mathematics achievement.