A 61-year-old man with history of bronchial asthma since childhood was admitted to our hospital for examination of eosinophilia and of lung infiltration seen in the chest radiograph. Allergic bronchopulmonary aspergillosis (ABPA) was diagnosed on the basis of the following findings: elevated serum IgE level, positive immediate skin reaction to Aspergillus antigen, the presence of precipitating antibodies against Aspergillus antigen, and central bronchiectasis. Oral prednisolone administration (30 mg daily) was started. During the course of reducing the prednisolone dose by up to 5 mg per day, pleural effusion appeared in the right lung. It was speculated that this eosinophilic exudative effusion was associated with a relapse of ABPA. After treatment with the dose of prednisolone increased to 20 mg per day and with oral itraconazole, the pleural effusion disappeared. We report a rare case of pleural effusion associated with ABPB on relapse.