An 82-year-old Japanese man with idiopathic pulmonary fibrosis (IPF) experienced dyspnea after using a waterproofing spray in a closed room. He presented with hypoxemia and his chest computed tomography showed additive bilateral diffuse ground-glass attenuation on fibrosis, which was diagnostic of an acute exacerbation of IPF (AE-IPF). Combined treatment with high-dose corticosteroids and immunosuppressants were ineffective, and he later died of respiratory failure. Autopsy findings showed diffuse alveolar damage with honeycombing. His medical history and autopsy histopathology suggested AE-IPF caused by the inhalation of a waterproofing spray.