To assess the efficacy of modified hydration on contrast-associated acute kidney injury (CA-AKI) in ST-segment elevation myocardial infarction (STEMI) after primary percutaneous coronary intervention (pPCI). A total of 438 patients were randomly assigned to 2 groups. The traditional hydration group (group I) was given at a rate of 1 ml/kg/h for 24 h, and the modified hydration group (group II) was given at a rate of 3 ml/kg/h in the first 4 h, and then reduced to 1 ml/kg/h for 12 h. 0.3 mg/kg of furosemide was given 1-h after hydration. The primary endpoint was the incidence of CA-AKI, and the secondary endpoint was the incidence of major adverse cardiovascular events (MACEs) during a median of 22.4 months (IQR 9.6, 32.6 months) follow-up. The incidence of CA-AKI was 8.7%. Among these, Group I was 9.1% and group II was 8.2%, respectively. There was no significant difference in CA-AKI and creatinine levels between the two hydration groups. Multivariable logistics regression analysis revealed that creatinine, white blood cells, and N-terminal pro-B-type natriuretic peptide were associated with CA-AKI. Moreover, CA-AKI was an independent predictor for all-cause death and cardiac death during the follow-up period. The modified hydration may reduce the incidence of CA-AKI, although this difference was not statistically significant. The relationship between CA-AKI and mortality strengthened as creatinine times above baseline increased. Mitigating the occurrence of CA-AKI may reduce all-cause death and cardiac death.© 2022. The Author(s).