Epistemological beliefs and argumentation are two important themes in science education, but research on the relationship between them is scarce. We treated epistemological beliefs in our study considering the cognitivist view of personal epistemology and included the justification, source, certainty, and development dimensions. We examined students' engagement in argumentation by considering expositional comments, oppositional comments, information seeking, and co-construction of knowledge. Sixth-grade students participated in this study. We measured the students' epistemological beliefs quantitatively before and after the argumentation activity to reveal any changes in their epistemological beliefs. We then used qualitative data to reveal how the students engaged in argumentation during whole-class discussions. Finally, we proposed possible connections between students' epistemological beliefs and their engagement in argumentation. MANOVA results showed no significant change in students' epistemological beliefs. Qualitative analyses revealed that students mainly used expositional comments during argumentation. Our findings suggested that the use of expositional comments can support the justification dimension of epistemological beliefs, but overuse of exposition can hinder other epistemological beliefs. Oppositional comments can feed the certainty and development dimensions of epistemological beliefs. Information-seeking can promote both the justification and source dimensions of epistemological beliefs. Finally, the use of co-construction of knowledge can improve both the justification and development dimensions of epistemological beliefs. The discussion and implication part addresses students' epistemological beliefs, engagement in argumentation, and the connection between epistemological beliefs and argumentation.