This research developed a Japanese version of the Implicit Theory of Willpower for Strenuous Mental Activities Scale (ITW-M) using data from two questionnaires completed by undergraduates. Study 1 ( N =2,493) demonstrated a factor structure similar to the original scale and partial measurement invariance across gender. Furthermore, implicit theories of willpower were significantly associated with self-control and life satisfaction, indicating the validity of this scale. Study 2 ( N =1,177) tested whether self-control demands moderated the effects of implicit theories of willpower on grades. The results showed that limited theories were associated with lower GPAs only among students taking heavy course loads, which suggests successful conceptual replications.