Background: A solid foundation in science is critical to students' success in the 21st century workforce, especially in fields related to science, technology, engineering, and mathematics (STEM). Therefore, high-quality science education is critical to prepare students for the challenges of the future. However, Emirati students have consistently performed poorly on international standardized science assessments, suggesting that the underlying factors contributing to this trend need to be understood. Therefore, the present study examined the relationship between motivational beliefs in science (i.e., science self-concept and intrinsic and instrumental motivation to learn science) and science achievement in Emirati early adolescents using a self-determination theory framework. Methods: A total of 7,915 Emirati eighth-grade students (Mean[subscript age] = 13.61 years, SD = 0.53) participated in the 2019 Trends in International Mathematics and Science Study (TIMSS). The TIMSS 2019 assessment measured students' motivational beliefs in science and their achievement in science. Path analysis and bootstrapping were used to examine the relationship between these variables and to test the mediating role of intrinsic and instrumental motivation to learn science in the relationship between science self-concept and science achievement. Results: The results of the study indicate that science self-concept is positively related to both intrinsic and instrumental motivation to learn science and science achievement. Intrinsic motivation to learn science was significantly related to science achievement, whereas instrumental motivation was not. Moreover, intrinsic motivation to learn science alone significantly mediated the relationship between science self-concept and science achievement. Conclusions: The study offers insights into the specific motivational beliefs associated with science achievement and highlights the importance of fostering positive science self-concept and intrinsic motivation in Emirati early adolescents. The study also suggests that interventions to promote positive science self-concept and intrinsic motivation to learn science may be particularly effective in improving science achievement in this population. These findings have important implications for educators and policymakers seeking to promote academic success and career opportunities for Emirati students in science.