Trends in International Mathematics and Science Study (TIMSS) 2019 data revealed that Grade 8 science teachers in several Asian countries (Chinese Taipei, Hong Kong SAR, Japan, and South Korea) reported lower job satisfaction levels than the international average. For example, while Japanese Grade 8 students ranked among the highest in science achievement on the TIMSS 2019, their science teachers reported the lowest job satisfaction composite scale score compared to the other 63 participating countries. Using teacher questionnaire data from TIMSS 2019, we utilized correlation analysis and multiple linear regression to uncover the answers to this research question: Which factors contribute to Japanese Grade 8 science teachers' job satisfaction? The results from the analysis indicate that working in a safe and orderly school environment was the strongest predictor of Japanese Grade 8 science teacher job satisfaction. The number of working hours, amount of perceived pressure exerted by their students' parents, participation in professional development focused on science curriculum, and adopting a constructivist orientation to science teaching were the other significant factors that predicted job satisfaction. Findings from this study have implications for Japanese educational policy stakeholders, school administrators, mentor teachers, science department leadership, and those invested in science teachers' professional development.