A growth creativity mindset is critical to the learning of creativity which is regarded as an important future skill. To cultivate such a positive belief and to understand what mechanisms may help improve growth mindset among children, we developed a story- and game-based learning system for creativity training, through which a five-class experimental instruction was conducted. Specifically, we aimed to examine the learning effect of growth creativity mindset and the relationship between mindful learning, mastery experience, and growth creativity mindsets in the context of game-based learning. Participants were 118 5th and 6th graders selected from six elementary schools in Taiwan. Led by a story called “Treasure Hunt,” which takes place across seven countries, the participants were scaffolded through interdisciplinary learning covering geography and creativity. The concerned variables were measured by 6-point Likert-type scales. Results of repeated measure analysis of variance revealed that the students’ perceived growth-external control mindset, but not the growth-internal control mindset, was significantly enhanced after the game-based learning. Moreover, a path model analysis indicated that mastery experience acts as a mediator between mindful learning and growth creativity mindset (especially the growth-internal control mindset). The results suggest that game-based learning in the context of a story helps in engaging students in mindful learning, achieving mastery experience, and strengthening a growth creativity mindset. This study also demonstrates the possibility of interdisciplinary design in game-based learning. The success of intervention and the theoretical framework proposed in the study provide insights to creativity education and the design of game-based learning.