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We report what is believed to be the first case of pulmonary Actinomyces graevenitzii infection presenting as organizing pneumonia. Fever and night sweats developed in a 69-year-old male. The only abnormal laboratory data were an elevated erythrocyte sedimentation rate and C-reactive protein level. On chest images, multiple consolidations with air bronchograms were seen in the bilateral lungs. Histological examination from lung biopsy revealed a pattern of organizing pneumonia with microabscesses, but definitive diagnosis was not obtained because culture from lung specimen was negative. A . graevenitzii was eventually identified in the lung biopsy specimen by detection of an Actinomyces-specific PCR product followed by 16S rRNA gene sequencing. The patient was treated with high-dose ampicillin intravenously for 1 month, followed by oral amoxicillin and clarithromycin for 6 months, and recovered. We suggest that actinomycosis can present as organizing pneumonia, and identification of infection by PCR analysis and rRNA gene sequencing is a useful strategy in cases that are difficult to diagnose.