Abstract Background New-onset atrial fibrillation (NOAF) is a common complication in patients with acute myocardial infarction (AMI) during hospitalization. Galectin-3 (Gal-3) is a novel inflammation marker that is significantly associated with AF. The association between post-AMI NOAF and Gal-3 during hospitalization is yet unclear. Objective The present study aimed to investigate the predictive value of plasma Gal-3 for post-AMI NOAF. Methods A total of 217 consecutive patients admitted with AMI were included in this retrospective study. Peripheral venous blood samples were obtained within 24 h after admission and plasma Gal-3 concentrations were measured. Results Post-AMI NOAF occurred in 18 patients in this study. Patients with NOAF were older (p