The purpose of this study was to reveal both the effects of problem-posing interventions on the mathematical creative ability of students and how students' creative self-efficacy in mathematics was related to their mathematical creative ability. Elementary school students (n = 205) were randomly assigned to one of two groups: problem-posing or control. Results showed the mathematical creativity for the problem-posing group increased (p < 0.05) more than for students in the control group (d = 0.77). Results from the Confirmatory Factor Analysis showed that mathematical creativity was a higher order factor that included mathematical creative ability and mathematical creative self-efficacy as first-order factors. Among the implications for this is that integrating problem-posing activities into elementary school mathematics instruction can foster mathematical creativity.