A 21-year-old woman presented with acute progressive dyspnea. Chest computed tomography (CT) revealed diffuse bilateral infiltrates. Based on the results of transbronchial lung biopsy (TBLB) and bronchoalveolar lavage fluid (BALF) and her clinical course, she was diagnosed as having acute eosinophilic pneumonia. We suspected that the disease was related to smoking because she had started smoking ten days before the onset of symptoms. Therefore, a cigarette-smoking challenge test was done with the patient's informed consent. After the challenge, eosinophilic pneumonia was documented by BALF and TBLB findings, which were similar to those detected on admission, without significant radiographic findings.