© 2014 Sports Medicine Australia. Objectives: Motivation in sport has been frequently identified as a key factor of young athletes' intention of doping in sport, but there has not been any attempt in scrutinizing the motivational mechanism involved. The present study applied the trans-contextual model of motivation to explain the relationship between motivation in a sport context and motivation and the social-cognitive factors (attitude, subjective norm, perceived behavioral control, and intention) from the theory of planned behavior (TPB) in an anti-doping context. Design: A cross-sectional survey was conducted. Methods: Questionnaire data was collected from 410 elite and sub-elite young athletes in Australia (Mean age [17.7. ±. 3.9. yr], 55.4% male, Years in sport [9.1. ±. 3.2]). We measured the key model variables of study in relation to sport motivation (Behavioral Regulation in Sport Questionnaire), and the motivation (adapted version of the Treatment Self-Regulation Questionnaire) and social cognitive patterns (the theory of planned behavior questionnaire) of doping avoidance. The data was analyzed by variance-based structural equation modeling with bootstrapping of 999 replications. Results: The goodness-of-fit of the hypothesized model was acceptable. The bootstrapped parameter estimates revealed that autonomous motivation and amotivation in sport were positively associated with the corresponding types of motivation for the avoidance of doping. Autonomous motivation, subjective norm, and perceived behavioral control in doping avoidance fully mediated the relationship between autonomous motivation in sport and intention for doping avoidance. Conclusions: The findings support the tenets of the trans-contextual model, and explain how motivation in sport is related to athletes' motivation and intention with respect to anti-doping behaviors.