Thoracic actinomycosis is a rarely-seen infection that is hard to diagnose, partly because of its variable presentations; it has often been misdiagnosed as a tumor or tuberculosis. Two cases of thoracic actinomycosis which had the same symptoms, signs and laboratory findings, have been reported in our ward. The radiographic findings showed the lesions as consolidation combining multiple peripheral cavities in both upper lobes. But they had different durations of disease course due to having been diagnosed on different occasions. The primary diagnosis was based on a bronchial washing for culture, then a lobectomy (case 1) and trans-thoracic biopsy (case 2). We compare these two cases and present the results of a literature review in this report. Through accumulated clinical experience with these cases, clinicians can improve the accuracy of their definite diagnosis of thoracic actinomycosis.