Procoagulant and prothrombotic states in patients with chronic atrial fibrillation (AF) are higher than those in patients with normal sinus rhythm. We assessed and compared serum gamma-glutamyltranferase (GGT) activity in elderly patients with nonvalvular AF and control participants with normal sinus rhythm. Consecutive patients (n = 81) with nonvalvular chronic AF and 210 age- and gender-matched control participants with normal sinus rhythm were retrospectively included in the study from the outpatient cardiology clinic. Presence of coronary artery disease, hypertension, gender, hyperlipidemia, diabetes mellitus, smoking status, glucose, total cholesterol, triglycerides, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and ejection fraction were comparable between the 2 groups (P > .05 for all). However, serum gamma-GGT activity was significantly higher (P = .003) in patients with AF compared with those without AF. We have shown that serum gamma-GGT activity is independently associated with chronic nonvalvular AF.