Based on self-determination theory and the theory of planned behavior, this study explored the predictors and behavioral mechanisms associated with Chinese scientists' public engagement with science. The results indicated that scientists' participation was associated with their levels of perceived autonomy, their attitudes toward participation and the media, subjective norms, perceived policies, their own efficacy, specific facilitating conditions, habits related to communication, and their willingness to engage. Under different levels of autonomy, these indicators had different association with scientists' willingness to engage and their reported participation in science communication activities. As levels of controlled motivation (or external requirement to communicate) increased, more negative effects related to willingness to participate or self-reported participation were identified, and amotivation (a lack of motivation) had a direct negative association with participation. The theoretical and practical implications of these findings are discussed.