This prospective study investigated the relationship between insulin resistance assessed using the homeostatic model assessment of insulin resistance (HOMA-IR) and the prognosis of acute pancreatitis (AP). A total of 269 patients with AP were recruited in this study. HOMA-IR scores were calculated using fasting insulin and plasma glucose levels. Patients were then categorized into the non-insulin-resistant group (HOMA-IR <2.5) and the insulin-resistant group (HOMA-IR ≥2.5). We performed multivariable logistic regression analysis to investigate the independent association between IR assessed using HOMA-IR and the severity of AP. We also conducted receiver operating characteristic analysis to investigate the predictive ability of HOMA-IR for severe AP. The proportion of patients with severe AP (according to the Atlanta classification) and the percentage of ICU admissions and mortality were higher in patients with insulin resistance than in those without insulin resistance. The area under the curve (AUC) of HOMA-IR for predicting severe AP was 0.719 (95% CI 0.59-0.85, P = 0.003). This value was not significantly different from the AUCs of other AP scoring systems such as CTSI, Ranson, and BISAP. Insulin resistance was the only independent factor for either ICU admission (OR 5.95, 95% CI 1.95-18.15, P = 0.002) or severe AP (OR 6.72, 95% CI 1.34-33.62, P = 0.020). Our findings suggest that the HOMA-IR score is an independent prognostic factor in patients with acute pancreatitis. This finding indicates that insulin resistance is potentially involved in the mechanism for severe AP.