This research was aimed to find the relationship between the fifth-grade students’ number sense and mathematical problem-solving. The participants of this study were 73 fifth grade students from a private Islamic school in Pekanbaru, Indonesia. This study applied a quantitative research method, namely a simple correlation. Instruments for measuring students’ number sense consist of 5 indicators; number concepts, multiple representations, effects of operations, equivalent expressions, and computing and counting strategies. While, the instruments to measure students’ problem-solving consist of 4 domains; numbers, fractions, geometry, and measurements. The results showed that there was a significant correlation between students’ number sense and mathematical problem-solving. After that, a correlation test was also conducted between each number sense indicator and each mathematical problem-solving domain. The indicator of computing and counting strategies has the highest correlation with measurement.