Objectives The purpose of the study was to examine the mediating effect of teaching aptitude in the effect of pre-service early childhood teachers' playfulness on teacher efficacy. Methods For this purpose, a survey was conducted on playfulness, teaching aptitude, and teacher efficacy among 215 students attending early childhood education departments at three universities located in Seoul and Gyeonggi Province. The collected data were subjected to Pearson's correlation analysis, multiple regression analysis, and the Sobel test to verify the mediating effect using SPSS Statistics 24,0. Results First, it was found that pre-service early childhood teachers' teacher efficacy had a significant positive correlation with both playfulness and teaching aptitude. Specifically, among the sub-factors of playfulness, cheerfulness and imagination were positively correlated with teacher efficacy, while all sub-factors of teaching aptitude showed a positive correlation with teacher efficacy. Second, in examining the mediating effect of teaching aptitude on the relationship between playfulness and teacher efficacy, it was confirmed that teaching aptitude had a complete mediating effect. The Sobel test conducted to verify the mediating effect showed that the effect of the mediating variable was significant. Conclusions Based on the results of this study, implications to improve the teacher efficacy of pre-service early childhood teachers in future early childhood teacher training courses were provided and educational action plans were discussed.