Conventional methods for diagnosing tuberculous (TB) pleurisy require either an invasive procedure or long periods of time. We performed interferon-γ (IFN-γ) assays on pleural fluid and evaluated a diagnostic utility to distinguish between TB pleurisy and non-TB pleural effusion. Interferon gamma levels were measured by QuantiFERON^®-TB gold (QFT-3G) tests. The tests and adenosine deaminase assays were performed on pleural fluid from 26 patients with TB pleural effusion and 99 patients with non-TB pleural effusion. The IFN-γ concentrations in the negative control samples were significantly higher in the TB pleurisy group than in the non-TB pleural effusion group. The sensitivity of the test was 100.0% and the specificity was 99.0%, using a 1.7 IU/ml cutoff point. These findings suggest that the pleural fluid IFN-γ assay could be an accurate and prompt method for diagnosing TB pleurisy.