A 73-year-old woman with polymyositis, who had received corticosteroids and immune-suppressive agents, was admitted to our hospital because of general fatigue and severe cough. Chest X-ray film and CT scan showed a large tumor shadow in the left upper lobe and several ground-glass opacities (GGOs) scattered in both lungs. As the white blood cell and C-reactive protein levels were elevated, pnueumonia was suspected and antibiotics were administered. Subsequently, Nocardia spp. was cultured from the sputum and pulmonary nocardiosis was established. She gradually recovered after sulfamethoxazole-trimethoprim (ST) administration. The pretreatment serum beta-D-glucan level was highly elevated and decreased in parallel with clinical feature. In general, ST should be administered for 6 months to treat pulmonary nocardiosis in a compromised host. It is possible that P3-D-glucan may be a useful marker to treat pulmonary nocardiosis in patients with polymyositis.