ObjectiveTo investigate whether lysyl oxidase(LOX) has significant relation to persistent atrial fibrillation(AF) with mitral valvular diseases. MethodsWe included 184 consecutive lone mitral valvular disease patients who needed surgery in our hospital between March 2012 and February 2014. Patients who had persistent AF formed the AF group, and those who still kept sinus rhythm(SR) comprised the SR group. In the AF group, patients were separated into two groups by the subgroup of mitral valvular disease(mitral stenosis and mitral regurgitation), then formed a MS+AF group and a MR+AF group. There were 97 patients with 44 males and 53 females at age of 52.76±11.35 years in the AF group and 90 patients with 48 males and 42 females at age of 47.95±14.22 years in the SR group. Blood specimens were obtained from patients for the first time peripheral venous blood after admitted to hospital. LOX levels were measured by ELISA test kits of LOX. ResultsAF was diagnosed in 51.87%(97/187) of lone mitral valvular disease patients. Mitral stenosis patients were easy to have AF(60.31% vs. 34.43%, P<0.05). The plasma level of LOX was significantly higher in the AF group than that in the SR group(73.78±25.42 IU/L vs. 51.05±18.96 IU/L，P<0.05). In the AF group, the LOX level in the mitral stenosis group was higher than that in the mitral regurgitation group(84.21±32.15 IU/L vs. 59.74±35.21 IU/L， P<0.05). Mitral stenosis patients more frequently had a history of stroke than mitral regurgitation patients did. AF correlated significantly with the level of LOX(r=0.124， P=0.036) and left atrial dimension(r=0.531，P=0.042). ConclusionWe validate and extend the hypothesis that increasing LOX level predicts an increasing risk of AF in mitral valvular diseases. Lysine oxidase is a potential diagnostic biomarker for AF. It is expressed significantly in mitral stenosis patients with AF especially.