Motivation to learn is an essential element in science learning. In this study, the role of career motivation in science learning was examined. In particular, first, a science motivation model that focused on career motivation was tested. Second, the role of career motivation as a predictor of STEM track choice was examined. Third, the effect of gender and academic year on science motivation was explored. The participants of the study were 626 high-school students. We used the Rasch analysis, structural equation modeling, logistic regression, MANOVA for the statistical analyses. It was found that career motivation has direct influences on several motivational factors in science learning, such as grade motivation, need for learning, self-determination, and self-efficacy. Moreover, career motivation was found to be a predictor of students' STEM track choice. Finally, there were substantial differences in science motivation across gender and academic years. Generally, females and students in higher academic years exhibited a lower level of science motivation. Female students especially showed a low level of career motivation. The findings suggest that it is important to facilitate students' career motivations to improve their science motivation and promote long-term scientific achievement.