A 29-year-old pregnant woman was referred to our hospital because of pneumonia that did not improve with antibiotic therapy. Chest X-P and CT scan showed ground-glass opacities and patchy consolidations in subpleural areas with nonsegmental distribution. She had facial erythema, heliotrope rash, and episodes of myalgia. From these findings, we diagnosed her with dermatomyositis-associated interstitial lung disease. Steroid pulse therapy following prednisolone 60 mg/day improved the interstitial lung disease and skin lesions. Anti-aminoacyl tRNA synthetase (anti-ARS) antibody was identified, and anti-PL-12 antibody was then also identified. Thus she was diagnosed with anti-ARS syndrome with anti-PL-12 antibody. She delivered a healthy baby. Fifteen months after delivery, her skin and muscle lesions recurred. Therefore cyclosporine was added to prednisolone, and the disease was then in control. We first report a case of interstitial lung disease with anti-ARS syndrome and anti-PL-12 antibody in a pregnant woman who was successfully treated and delivered a healthy child.