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Abstract Background Actinomycosis is a rare bacterial infection caused by Actinomyces. The symptom of actinomycosis is nonspecific and radiological images present as a slow-progressive mass lesion similarly to malignancies. Thus, it is difficult to distinguish pulmonary actinomycosis from malignancies. Case presentation A 74-year-old male who had esophageal cancer and a pulmonary mass that was positive for 18F–fluorodeoxyglucose positron emission tomography/computed tomography was initially diagnosed with esophageal cancer with a lung metastasis because he was asymptomatic. However, aspiration of pleural effusion revealed that the pulmonary lesion was actinomycosis. Conclusion We present a case of pulmonary actinomycosis mimicking a lung metastasis from esophageal cancer. Diagnosis of asymptomatic pulmonary actinomycosis is difficult, and needle aspiration could be useful for a definitive diagnosis of pulmonary actinomycosis.