The different motivations postulated by the Self-Determination Theory have proved to be meaningful to predict the level of engagement in a wide variety of life domains. The present research examines the relation between the different forms of self-determined motivation and behavioral automaticity of 12 behaviors associated with different life domains. Following 1743 measurements of self-determination (using a short version of the situational motivational scale, SIMS8), behavioral automaticity (using the self-reported behavioral automaticity index, SRBAI), and behavioral frequency (self-reported number of executions in a unit of time) for 12 various common behaviors collected on 315 young adults ( Mage = 20.60 ± 2.87 years) through an online survey, the results of crossed linear mixed models indicated that self-determined motivations are more associated with behavioral automaticity than nonself- determined motivations (intrinsic motivation: β = 0.13, p < .001, identified extrinsic motivation: β = 0.13, p < .001; external extrinsic motivation : β = 0.08, p < .001; amotivation: β = 0.02, p = .433). Furthermore, self-determination played a moderating role between the repetition of behaviors and behavioral automaticity (β = 0.06, p < .002) suggesting that self-determination facilitated automatization,as high level of behavioral automaticity was achieved with less frequent behaviors when behaviors were performed for highly self-determined (β = 0.41, p < .001) than weakly self-determined reasons (β = 0.29, p < .001). The applications of these findings for learning and habit formation are discussed.