Conventional methods for diagnosing tuberculous (TB) pleurisy require either an invasive procedure or long periods of time. We performed QuantiFERON^®-TB Gold (QFT-3G) tests on pleural fluid and evaluated a diagnostic utility for distinguishing between TB pleurisy and non-TB pleural effusion. The QFT-3G tests and adenosine deaminase assays were performed on pleural fluid from 9 patients with TB pleural effusion and 35 patients with non-TB pleural effusion. The interferon-γ concentrations in the negative control samples were significantly higher in the TB pleurisy group than in the non-TB pleural effusion group. The values were all higher than 3.2 IU/ml in the 9 TB pleurisy group (median: 7.0 IU/ml). On the contrary, the values were all less than 0.7 IU/ml in the 35 non-TB pleural effusion group (median: 0.07 IU/ml). These findings suggest that the pleural fluid QFT-3G assay could be an accurate and prompt method for diagnosing TB pleurisy.