Rheumatoid arthritis-related interstitial pneumonia with a usual interstitial pneumonia (RA-UIP) has a poor prognosis and a new treatment strategy is required. The antifibrotic agent nintedanib reduces the annual rate of decline in forced vital capacity (FVC) in idiopathic pulmonary fibrosis (IPF) patients. Recently, the potential efficacy of antifibrotic agents against chronic progressive fibrotic diseases including RA-UIP has been attracting attention. A 74-year-old man diagnosed with IPF on high-resolution computed tomography (HRCT). His FVC was decreasing over time, and his exertional dyspnea and cough had progressed with progression of reticulation on imaging. He was treated with nintedanib, which resulted in decreased coughing together with a reduction in FVC decline, from -11.6%/year to -5.2%/year. A swollen joint appeared eight months after this intervention, and he was diagnosed with rheumatoid arthritis. In this patient, nintedanib was effective against RA-UIP. This is the first case in which nintedanib was shown to be effective for RA-UIP.