<b><i>Objective:</i></b> Atrial fibrillation (AF) is common in acute myocardial infarction (AMI), and galectin-3 is possibly involved in its occurrence. Galectin-3 has been shown to play a central role in fibrosis and tissue remodeling and has a role in inflammatory and proliferative responses. The aim of our study was to measure galectin-3 levels in patients with myocardial infarction and to compare its levels in patients with or without AF, in order to investigate the potential predictive role of galectin-3 in this setting. <b><i>Subjects and Methods:</i></b> The study included 51 consecutive AMI patients with AF; 27 AMI patients (52.9%) had permanent/persistent AF, and 24 patients (47.1%) had paroxysmal AF. Thirty-eight consecutive AMI patients without AF were used as a control group. Blood samples were obtained from venous blood on the third day after reperfusion. <b><i>Results:</i></b> Patients with AF had higher levels of C-reactive protein (<i>p</i> &#x3c; 0.01) and galectin-3 (<i>p</i> &#x3c; 0.05) than those without AF. Patients with high galectin-3 had 4.4 times greater odds of having AF. Galectin-3 levels were lower in patients without AF (<i>p</i> &#x3c; 0.01) than in those with permanent/persistent AF. <b><i>Conclusion:</i></b> AMI patients with AF had higher levels of galectin-3 than those without this arrhythmia. This biomarker of inflammation and fibrosis could be a potential target for treating AMI patients at high risk.