Abstract: AIM:To investigate the significance of matrix metalloproteinases-9 (MMP-9), tissue inhibitor of metalloproteinase-1 (TIMP-1), transforming growth factor-beta 1 (TGF-β1) and basic fibroblast growth factor (bFGF) serum level related to atrial structural remodeling in atrial fibrillation (AF) patients without structural heart disease. METHODS: Serum samples were taken from, respectively, left atrium and right atrium of 42 AF patients without structural heart disease and 17 paroxysmal supraventricular tachycardia or patients with Wolff-Parkinson-White (WPW) syndrome who underwent catheter ablation. Pre-ablation plasma concentrations of MMP-9, TIMP-1, TGF-β1 and bFGF were evaluated by ELISA. Left atrial diameter (LAD) was detected by echocardiography. RESULTS: LAD in AF group (36±7) mm was statistically higher than in control group (31±4) mm. MMP-9 serum level of the left atrium in the AF group (3037±804) pg/ml was statistically higher than in the control group (2439±663) pg/ml (P<0.01) and the level in the right atrium (2635±930.38) pg/ml (P<0.05). Right atrium MMP-9 levels in the AF group (2635.35±930.38) pg/ml were similar to the control group (2762.34±802.53) pg/ml (P>0.05). TIMP-1 level in AF group was statistically lower than in control group (P<0.05) and TGF-β1 level in the AF group was statistically higher than control group (P<0.05). No significant difference in bFGF level was found between AF and control groups. MMP9 serum level and LAD in AF group was linearly correlated (0.447, P<0.01). CONCLUSIONS: MMP-9, TIMP-1 and TGF-β1 are closely related to the occurrence of AF and can be used to predict the structural remodeling of left atrium in patients with AF.