Objective:To investigate the cell-free DNA amount and DNA integrity in benign and malignant effusions. Methods:The samples of twenty-eight benign effusions and thirty-eight malignant effusions were collected and analyzed for the DNA amount and integrity by the real-time ALU-qPCR(115 bp,247 bp). Results:The content of ALU247 fragment is statistically different between two groups(P < 0.05),while there is no statistical difference between the two groups in the content of ALU115. When the DNA integrity was compared, the malignant samples had a relative higher DNA integrity(P < 0.05). AUC of ROC for DNA integrity was 0.716(P < 0.01). Conclusion:Malignant effusion samples had a significantly higher amount of long DNA and DNA integrity, and DNA integrity may be a potential biomarker to distinguish malignant effusions from benign effusions.