This study explores the intersection role of students' epistemic beliefs and gender in argumentative essay writing. In total, 148 undergraduate students from a Dutch university followed an argumentation module, filled out the epistemic beliefs survey, and wrote an argumentative essay. Results showed that students' beliefs about the Internet-specific justification of knowledge did not influence essay performance. On the other hand, beliefs about the nature of scientific knowledge influenced their argumentative essay writing. Overall, there were no gender differences in argumentative essay writing. However, female students outperformed male students in taking a position on the topic. The interaction effects of beliefs about the Internet-specific justification of knowledge and gender in argumentation performance were neutral. There was, however, an intersection effect of students' epistemic beliefs about the nature of scientific knowledge and their gender in argumentation performance. We discuss these results and provide suggestions for future research.