Objective: Atrial fibrillation (AF) is the most common cardiac arrhythmia in clinical practice. Unfortunately, the sensitive serum biomarkers of atrial remodeling in AF remain unclear. The aim of this study was to determine sensitive serum markers for estimating atrial structural remodeling of AF. Methods: Right and left atrial specimens were obtained from 90 patients undergoing valve replacement surgery. The patients were divided into the sinus rhythm(n = 30),the paroxysmal atrial fibrillation(n = 30),and the persistent atrial fibrillation (n = 30) groups. CIB1, calcineurinA, calcineurinB,nuclear factor of activated T3(NF-AT3),nuclear factor of activated T4(NF-AT4), collagen Ⅰ and Ⅲ protein expression in atria were measured. We also tested the levels of the carboxyl-terminal peptide of pro-collagen Ⅰ(PICP),the N-terminal typeⅠprocollagen propeptides, the N-terminal type Ⅲ procollagen propeptides, and TGF-β1 in serum using an enzyme immunosorbent assay. Results: Key protein expression in calcineurin system was increased in the AF groups,especially in the left atrium. In patients with AF, the expression levels of nuclear NF-AT3 and NF-AT4 were correlated with those of collagens Ⅰ and Ⅲ in the atria and with PICP and TGF-β1 in blood. Conclusion:These data support the hypothesis that PICP and TGF-β1 levels may be sensitive serum biomarkers to estimate atrial structural remodeling with at AF.