Abstract: ［Abstract］Objective To investigate the clinical application value of liquid based cytology（LBC） in differential diagnosis of benign and malignant hydrothorax and ascites．Methods　Nine hundreds and forty-seven cases of hydrothorax and ascites samples， including 752 cases of hydrothorax and 195 cases of ascites， were collected. Liquid based cytology（LBC） test and conventional cytology（CC）test were performed to differentially diagnose benign and malignant hydrothorax and ascites， and the difference in the quality and satisfaction of cell slide preparation and the diagnostic results were compared between the two cytology tests．Results（1） Cell slide prepared with CC: the positive cells were few and scattered and had more overlap， the cell distribution was thick and uneven， the background was not clear and often interfered by red blood cells and inflammatory exudate. Cell slide prepared with LBC: the positive cells were more and concentrated and had no overlap， the cell distribution was uniform and in monolayer， the background was clean and clear. The satisfaction rate of slide preparation with CC and LBC was 86.5% and 95.2%， respectively（P＜0.05）. （2）In the total 947 cases of hydrothorax and ascites，the positive rate（27.2%）of LBC test was a little higher than CC test（27.2% vs. 24.6%），but the difference had no statistical significance（P＞0.05）. Conclusion　Liquid based cytology is better than conventional cytology in the quality and satisfaction of the cell slide preparation of hydrothorax and ascites samples， and has a little higher positive diagnostic rate of malignant hydrothorax and ascites.