Objective: The purpose of this study was to clarify the influences of constructivist educational beliefs and eco-friendly teaching attitudes on early childhood teachers' mathematics teaching efficacy. This study also examined the mediating effect of eco-friendly attitudes on the relationship between the other two variables. Methods: A total of 399 teachers teaching 3,4 and 5-year-olds in Seoul, Gyeonggi and Incheon participated in this study. The data were analyzed using the SPSS Win 21.0 program and the Sobel test. Results: First, mathematical teaching efficacy of early childhood teachers was significantly correlated with constructivist educational beliefs and eco-friendly teaching attitudes. Second, with teacher 's career as the control variable, constructivist educational beliefs have more influence in mathematical teaching efficacy than the other variable. Third, eco-friendly teaching attitude partially mediated between the other two variables. Conclusion/Implications: The results of this study imply that constructivist educational beliefs and eco-friendly teaching attitudes are important factors on mathematics teaching efficacy. It is expected that it will be used as basic data for various programs that increase constructivist educational beliefs and eco-friendly teaching attitudes.