The advantages of aggressive hydration compared to conservative hydration within 24 h for acute pancreatitis (AP) remain controversial in adult patients. A meta-analysis was undertaken to investigate whether aggressive strategies are more beneficial.We searched (on February 1, 2021) PubMed, Embase, and the Cochrane Library for eligible trials that assessed the two therapies and performed a meta-analysis. The primary endpoint was in-hospital mortality. Secondary outcomes were adverse events (e.g., renal failure and pancreatic necrosis) within 24 h of treatment.Five randomized controlled trials and 8 observational trials involving 3127 patients were identified. Patients with severe pancreatitis showed significant difference of in-hospital mortality (OR 1.75; 95% CI 1.32-2.33) in aggressive hydration group, which were less susceptible to study type and age. Patients with severe pancreatitis were likely to develop respiratory failure (OR 5.08; 95% CI 2.31-11.15), persistent SIRS (OR 2.83; 95% CI 1.58-5.04), renal failure (OR 2.58; 95% CI 1.90-3.50) with significant difference. A longer hospital stay was observed in patients with severe pancreatitis (WMD 7.61; 95% CI 5.51-9.71; P < 0.05) in the aggressive hydration group. Higher incidence of pancreatic necrosis (OR 2.34; 95% CI 1.60-3.42; P < 0.05) was major susceptible to observational studies, old patients and mild pancreatitis.Compared to conservative hydration, aggressive hydration increases in-hospital mortality and the incidence of renal failure, pancreatic necrosis with relatively strong evidence. Further investigation should be designed with a definitive follow-up period and therapeutic goals to address reverse causation bias.Copyright © 2022. Published by Elsevier B.V.