This study examined how motivational factors (i.e., self-concept in science, enjoyment of science, and instrumental value of science) predict science, technology, engineering, and math (STEM) career aspirations using a nationally representative sample of 5,611 fifteen-year-old students (49.4% female) in the United States. The findings demonstrated that the motivational factors, particularly enjoyment and instrumental value, are important predictors of STEM career aspirations even after controlling for socioeconomic status (SES), STEM career awareness, and science achievement. The findings also demonstrated that, although the motivational factors operate slightly differently across gender, they seem to function similarly across racial and ethnic groups. The findings have important implications for how to promote STEM career aspirations.