Purpose: The purposes of this study were (a) to investigate the relationships between perceived motivational climate and athlete effort, and (b) to examine the mediating effects of sport failure tolerance on the relationships between motivational climate and athlete effort. The conceptual model of this study assumed that motivational climate would affect sport failure tolerance and these would, in turn, affect athlete effort through the mediation of the sport failure tolerance. Methods: A total of 321 Korean active high school student athletes from 6 sports participated in the study (Mage=17.83years, SD=±.80). The participants completed four questionnaires: a demographic questionnaire, Sport Failure Tolerance Questionnaire, Perceived Motivational Climate in Sport Questionnaire, and Athlete Effort Questionnaire. Results: The results of the final model indicated that competitive climate was positively related to task difficulty (.21), whereas after failure emotion and behavior factors did not. Mastery climate was significantly related to all three dimensions of sport failure tolerance (task difficulty .39, after failure emotion .39 and failure behavior .57). Task difficulty was only significantly related to athlete effort (.14). Mastery climate was significantly related to athlete effort (.31). Significant indirect effects were observed. The bootstrapping results indicated that the relationship between mastery climate and athlete effort was mediated by task difficulty, after failure emotion and failure behavior. Conclusion: The findings of this study contribute to the current understanding of the relationships between perceived mastery climate and athlete effort and shed light on the important roles of sport failure tolerance.