Objectives We investigated whether the serum markers of collagen turnover differed in various forms of atrial fibrillation (AF) and in sinus rhythm (SR) in humans. Background Structural alterations and fibrosis have been implicated in the generation and perpetuation of AF. Methods Serum C-terminal propeptide of collagen type-I (CICP), C-terminal telopeptide of collagen type-I (CITP), matrix metalloproteinase-1, and tissue inhibitor of matrix metalloproteinases-1 were measured as markers of collagen synthesis and degradation in 70 patients with AF and 20 healthy control subjects in SR. Results C-terminal propeptide of collagen type-I and CITP were significantly higher in AF patients than in control subjects (91 ± 27 ng/ml vs. 67 ± 11 ng/ml, p < 0.001 and 0.38 ± 0.20 ng/ml vs. 0.25 ± 0.08 ng/ml, p < 0.001, respectively). Persistent AF patients had higher levels of CICP (105 ± 28 ng/ml vs. 80 ± 21 ng/ml, p < 0.001), but not CITP, compared with those with paroxysmal AF. Patients with persistent AF had lower levels of matrix metalloproteinase-1 but increased levels of tissue inhibitor of matrix metalloproteinases-1 compared with patients with paroxysmal AF (11.90 ± 4.79 ng/ml vs. 14.98 ± 6.28 ng/ml, p = 0.03 and 155 ± 45 ng/ml vs. 130 ± 38 ng/ml, p < 0.001, respectively). Tissue inhibitor of matrix metalloproteinases-1 levels were significantly lower in control subjects compared with those in both paroxysmal and persistent AF patients (102 ± 15 ng/ml vs. 130 ± 38 ng/ml vs. 155 ± 45 ng/ml, respectively, p < 0.001). Conclusions Serum markers of collagen type-I turnover differed significantly between patients with AF and SR. Furthermore, these markers also differed significantly between paroxysmal and persistent AF patients, suggesting that the intensity of the extracellular synthesis and degradation of collagen type-I may be related to the burden or type of AF.