A 76-year-old man had suffered from asthma since age 6. His asthma had recently worsened due to pneumonia. At a local clinic, he was given steroids and antibiotics for more than a week. Although his pneumonia improved, his asthma was not controlled, so he was admitted to our hospital. Steroid therapy was administered for about 2 weeks in an attempt to treat the asthma. From a chest x-ray film and CT scan it was apparent that multiple nodules had appeared in the lower lobes of both lungs. We performed bronchoscopy and Nocardia species were detected in both lower lobes of the lung from bronchoalveolar lavage. Pulmonary nocardiosis was diagnosed. We started treatment with sulfamethoxazole and trimethoprim. While the fever was reduced and the appearance of the chest X-ray improved, appetite loss became serious, so we changed the antibiotic regimen to imipenem/cilastatin and amikacin. Following this change in medication, the patient's fever increased again and the chest X-ray findings regressed, so we changed his antibiotic regimen to minocycline. All symptoms improved thereafter. Nocardiosis often occurs in immunocompromised patients. Mortality is about 35%, so rapid diagnosis and appropriate treatment is necessary, but not always possible due to difficulties in diagnosis. The onset of lung nocardiosis is usually subacute. This case was caught comparatively early, because of the previous steroid treatment.