Atrial fibrillation (AF) is the most frequently encountered arrhythmia and is largely associated with cognitive decline. Obstructive sleep apnea (OSA) may lead to cognitive decline through chronic sleep fragmentation and intermittent hypoxemia. Does the association between these pathologies increase cognitive impairment's likelihood? Determine the prevalence of cognitive deficit in AF patients and to identify the predictive factors of this disorder. The study concerned 81 patients with non valvular AF. Patients with a history of stroke were not included. The cognitive performance was assessed by evaluating different parameters: Memory, attention and executive functions (inhibition, shifting, updating/monitoring information). A cognitive deficit was considered if at least one of these parameters was defective. The average age was 66,2 ± 9.7 years old. A detailed questioning regarding cognitive function objectified that 78% of patients had cognitive deficit. An age greater than 68 years, was significantly related to cognitive disorders ( P = 0.002). Symptomatic AF with EHRA class III or IV, was statistically associated with cognitive impairment ( P = 0.014). Referring to polygraph's results, 74 patients (91.4%) had OSA. Moderate and severe OSA (AHI > 15) were significantly associated with cognitive impairment ( P = 0.004). Total desaturation time under 90% was correlated with cognitive decline ( P = 0.003) with a limit value for predicting cognitive deficit, of 4 minutes (sensitivity = 70%, Specificity = 68%). The multivariate study found that predictors of cognitive impairment in AF patients were: age > 68 years( P = 0.012, OR = 6.3), AHI > 15 ( P = 0.049, OR = 3.8) and an EHRA class III or IV ( P = 0.025, OR = 5). Our study revealed that moderate to severe OSA is an independent predictive factor of cognitive impairment in AF patients. Thus, treating OSA by continuous airway pressure may have a beneficial effect on cognitive function.