Prior physics education studies have established a positive relationship between students' learning gains and their epistemological views measured at single time points (i.e., either before or after instruction). These studies, albeit informative, miss the dynamic nature of students' views about physics. In this study, we seek to investigate students' epistemological shifts in relation to their learning gains. Students' epistemological shifts were measured by the difference in their performances on the Colorado Learning Attitudes about Science Survey (CLASS) before and after a traditionally taught introductory mechanics course (δ_CLASS). Student learning gains were measured by their normalized gains on the Force Concept Inventory (FCI). Results revealed a large variation in students' epistemological change after instruction despite a near-zero shift on average. Also, while no significant overall relation was detected between δ_CLASS and FCI normalized gains, the FCI results seemed to be sensitive to epistemological changes among the lower-end students who remained below average on both the pre and post CLASS. In this case, those who experienced a positive epistemological shift achieved higher conceptual gains than those otherwise.