Background: There is not much data on matrix metalloproteinase neutrophil gelatinase-associated lipocalin (MMP-NGAL) complex in patients with atrial fibrillation (AF). Aim: The aim of the study was to assess the value of MMP-NGAL complex in predicting AF recurrence after electrical cardioversion. Methods: The serum levels of NGAL, cystatin C, interleukin-6, high-sensitivity C-reactive protein, copeptin, MMP-NGAL complex, matrix metalloproteinase 2, tissue inhibitor of metalloproteinase 1, Von Willebrand factor, B-type natriuretic peptide and the urinary level of NGAL were evaluated before cardioversion. Results: A total of 83 patients with persistent AF were enrolled in the study. Left atrial diameter (LA) ≥4.5 cm was significantly associated with AF recurrence at follow-up (p = 0.009). In selected 39 obese patients, MMP-NGAL complex was associated with AF recurrence (p = 0.03). If the concentration of MMP-NGAL complex increased by 1 ng/ml, the odds of AF recurrence increased by 4% (OR 1.04; CI: 1.00-1.08; p = 0.03). MMP-NGAL complex did not correlate with AF recurrence in patients with a first episode of AF, in patients ≥65 years of age and in patients with a LA ≥4.5 cm or with chronic kidney disease. Conclusions: It is known that the greater the BMI at baseline, the higher the likelihood of progression from paroxysmal to permanent AF. However, European Society of Cardiology (ESC) guidelines do not consider obese patients a population with a low likelihood of success of cardioversion. That is why we need a sensitive marker to predict sinus rhythm maintenance in such a population. We found that MMP-NGAL complex may predict AF recurrence after successful cardioversion in obese patients.