Several scoring systems for clinical prediction of the severity of acute pancreatitis (AP) have been proposed. Yet, there is still a need for an easy-to-measure biomarker. Osteopontin (OPN) may be released to the circulation early during tissue injury, but the significance of OPN in AP has not yet been established. We aimed to evaluate plasma levels of OPN in relation to the severity of AP. In 39 individuals with confirmed AP, plasma was collected on the day of admission and consecutively for three days thereafter. Sex- and age-matched healthy blood donors (n = 39) served as controls. Plasma OPN was measured by a commercial enzyme-linked immunosorbent assay. At admission, patients with AP displayed higher OPN, 156.4 ng/mL (IQR 111.8-196.2) compared to controls, 37.4 ng/mL (IQR 11.7-65.7) (p < 0.0001). However, OPN levels on admission could not discriminate between mild and moderate-to-severe disease (132.6 ng/mL vs. 163.4 ng/mL). Nevertheless, the changes in OPN within 24 h of admission and Day 2/3 were higher among patients with moderate/severe AP (33.7%) compared to mild AP (-8.1%) (p = 0.01). This indicates that OPN is a relevant biomarker reflecting tissue injury in AP. The increase in OPN over time suggests that serial OPN measurements could contribute to the early detection of at-risk patients. Prospective studies assessing OPN in relation to outcome in AP are warranted.