Objective   To investigate the correlation of pleural effusion and serum levels and the ratio of adenosine deaminase (ADA), total protein (TP) and lactate dehydrogenase (LDH) in the diagnosis of tuberculous pleurisy. Methods    Fifty cases of tuberculous pleurisy patients (tuberculosis group) and twenty cases of hepatic hydrothorax (control group) were randomly selected and involved in this study. The ADA, total protein (TP), LDH in pleural effusion and serum were detected and the corresponding ratios were calculated. Results   The levels of ADA, TP and LDH in tuberculosis group and their ratios of the pleural fluid to serum were significantly higher than that of control group (P<0.05).  The pleural fluid ADA levels were linear positive correlated with TP and LDH levels in tuberculosis group (P < 0.01). The serum ADA was linear positive correlated with TP (P < 0.01), and no correlation with LDH in tuberculosis group (P > 0.05). The ratio of ADA in pleural effusion and serum levels was positively correlated with the ratio of LDH (P < 0.01), but no correlation with the ratio of TP (P > 0.05). Conclusion The ratio of ADA, TP and LDH in the pleural effusion and serum has the important clinical significance in diagnosis of tuberculous pleurisy.