We report here a case of acute hypersensitivity pneumonitis induced by an oil fan heater. A 57-year-old man was admitted to our hospital because of fever, nonproductive cough, and dyspnea. Paeccilomyces variotii and Paeccilomyces nivea were identified from an oil fan heater in his house. The result of an environmental challenge test was positive. Intradermal reaction and precipitin results to sugar antigen of those fungi were positive only in the patient. This is the first described case of acute hypersensitivity pneumonitis caused by an oil fan heater.