Background: Atrial fibrillation (AF) is an arrhythmia characterized by abnormal and chaotic electrical pulse generation observed in the upper heart chambers. This condition is the most common heart rhythm disorder, with prevalence rates of 2.3‐3.4% in the general population. Atrial fibrillation often leads to the development of blood clots, heart failure, other cardiovascular complications, hospitalizations, mortality, and overall increased healthcare expenditures.Objective: To assess patients' knowledge and adherence levels to oral anticoagulant therapy in patients with atrial fibrillation. Subjects and Methods: Setting: This study was conducted at outpatient cardiac clinics at Elmery hospital in Alexandria University. Subject: The study included a purposive sample composed of 55 patients with atrial fibrillation on oral anticoagulant therapy. Data were collected using the following tools: -Tool I: Patient's interviewing questionnaire. Tool-II Morisky Medication Adherence Scale (MMAS).Results: 58.2% of the studied patients age were≥50years. 58.2% were males and 85.5 of them were married. 61.8% had were illiterate and primary education, 72.7% were an employee and 65.5% live in rural areas. 65.5% of the studied patients mentioned that they had insufficient income. 63.6% of the studied patients had unsatisfactory level of knowledge regarding OACs. 50.9% of the studied patients had high level of adherence, 29.1% of the studied patients had medium level of adherence while 20% of the studied patients had low level of adherence regarding oral anticoagulant therapy. There was statistical significance relation between patients' total level of knowledge and their age, education level and treatment regimen. There was statistical significance relation between patients' total adherence level and their age, education level, treatment regimen, monthly income and residence. There was a positive relation between patients' total level of knowledge and their total adherence level. Conclusion: Based on the findings of the current study, it can be concluded that, more than three fifth of the studied patients had unsatisfactory total knowledge score about OAC, and more than half of them had good adherence levels (63.6%, and 50.9% respectively). Results highlighted positive significant relations between patients' adherence to OAC and their level of knowledge.