Objective: This study aims to identify developmental differences in the theory of mind (ToM) and executive function (EF) performances between 1st～2nd and 3rd～4th grade students, and to examine the effects of EF on ToM. Methods: A total of 35 1st～2nd grade students and 30 3rd～4th grade students participated in this study. A battery of ToM and EF tasks, as well as verbal ability tasks, were administered for each student. Mothers were requested to complete a questionnaire inquiring about children’s ToM and EF. Data were analyzed using repeated-measures analysis of variance, correlations, and hierarchical regressions. Results: First, the 3rd～4th grade students outperformed the 1st～2nd grade students on both ToM and EF tasks. Second, the correlations between performance-based measures and maternal ratings of ToM and EF were not significant. Finally, after controlling for the effects of verbal ability, 1st～2nd grade students’ EF performances were found to significantly influence their ToM performances. On the other hand, 3rd～4th grade students’ EF performances did not have a significant effect on their ToM performances. However, in terms of the rating measure, the association between ToM and EF was significant for both 1st～2nd and 3rd～4th grade students. Conclusions: The findings suggest that EF influences ToM; however, this association weakens across the elementary school years. Therefore, to promote ToM in middle childhood, a different approach based on grades is required.