Catheter ablation is a widely accepted therapy for atrial fibrillation (AF), of which stroke is a major complication. A stroke after catheter ablation has been reported in numerous studies not only in the acute phase but also in the chronic phase. A 66-year-old man with drug refractory paroxysmal AF underwent catheter ablation. Fourteen months later, the patient was diagnosed with cerebral infarction. Transesophageal echocardiography detected an ovoid mass on the anterior aspect of the right superior pulmonary vein atrium, where the previous ablation was performed. We report a very rare case of left atrial thrombus formation required surgical treatment 14 months after cryoballoon ablation.Careful follow up with multimodalities is necessary for the detection and diagnosis of chronic phrase thrombus formation.