Math anxiety (MA) is a prevalent academic anxiety that can affect student mental health and academic performance worldwide. Using a very large sample of students in grades 7 to 10 (N = 7172) in Qatar, the present study examined the associations among gender, math anxiety, and attitudes towards Science, Technology, Engineering, and Mathematics (STEM). In addition, the factorial structure of the "Student Attitudes towards STEM Survey" (STEM-S) was examined. The results confirmed the three-factor structure of the STEM-S, with good-to-excellent reliabilities. Females exhibited higher levels of math anxiety and more negative attitudes towards the STEM domains than males across all grade groups. In addition, strong negative correlations were found between math anxiety and STEM-related attitudes. Multiple linear regression analysis revealed negative associations between math anxiety and attitudes towards STEM when gender was partialized out. In stark contrast, there were close to zero associations between gender and STEM-related attitudes when math anxiety was partialized out. Consistently, structure equation modelling reported that math anxiety mediated the associations between gender and STEM-related attitudes. Therefore, providing psychological interventions for high math-anxious female students may improve their representation in STEM-related education and occupations.