Background:MicroRNAs (miRNAs) are widely involved in the regulation of physiological processes, such as cell proliferation, differentiation, apoptosis, angiogenesis, and lipid metabolism. They might be associated with the pathological process of atrial fibrillation (AF). The purpose of our study is to investigate whether plasma miRNA-155 levels have a relationship with AF recurrence.Methods:A total of 110 patients with AF were studied, all with successful cardioversion. We measured the expression of plasma miRNA-155 in the recurrent group (n = 30) and in the nonrecurrent group (n = 80) by quantitative reverse transcription–polymerase chain reaction (qRT-PCR). In addition, the serumal levels of B-type natriuretic peptide (BNP), total cholesterol (TC), and fasting blood glucose (FBG) in the groups were determined by using an automatic biochemical analyzer; and an immunoenzymatic method was applied to determine the serumal levels of tumor necrosis factor-α (TNF-α), C-reactive protein (CRP), and interleukin-6 (IL-6). The left atrial diameter (LAD) and left ventricular ejection fraction (EF) of all patients were measured by using echocardiography.Results:Our RT-PCR analysis found that miRNA-155 was significantly upregulated in the recurrent group compared with the nonrecurrent group. These increases of LAD and the levels of BNP, TNF-α, CRP, and IL-6 in the recurrent group were also revealed to be relative to those in the nonrecurrent group. There were no differences in the levels of TC and FBG, as well as in EF, between the groups. Moreover, miRNA-155 expression was observed to correlate positively with these outcomes of LAD, BNP, TNF-α, CRP, IL-6, and LAD. A diagnostic significance of predicting AF recurrence for plasma miRNA-155 was elucidated via ROC curve analysis.Conclusions:Our findings revealed that plasma miRNA-155 can present an ability to calculate AF recurrence after cardioversion.