The present two studies investigated whether students' development of epistemic beliefs about the educational sciences (study A; N = 152) and linguistics (study B; N = 150) can be affected by authentic learning activities in an out-of-school lab (OSL). OSLs aim to engage students in authentic activities that attempt to simulate the ways how scientists gather new knowledge, making an impact on students' epistemic beliefs likely. To test this assumption, the two (quasi-)experimental studies each compared a highly authentic with a less authentic activity and assessed students' epistemic beliefs before and after the students' visit to the OSL. We also analyzed how students' epistemic beliefs relate to their perceived authenticity of the learning activity, their situational interest, and their knowledge acquisition. The findings suggest that authentic activities in OSLs have no effect on students' epistemic beliefs, as students in both conditions either developed more sophisticated beliefs (study A) or changed their beliefs in the less authentic condition only (study B). Correlational analyses further show that students' epistemic beliefs about the texture of knowledge are negatively associated with both their perceived authenticity of the learning activity (studies A and B) and their situational interest (study A only). In contrast, students' epistemic beliefs about the variability of knowledge are positively correlated with their perceived authenticity and their knowledge acquisition (both in study A only). The findings are discussed in light of previous research on both students' epistemic beliefs and authentic learning in OSLs.