To study the value of high-fluorescent cell for the screening of malignant hydrothorax or ascites. The clinical diagnosis results and hydrothorax or ascites specimens of 400 outpatients registered from January to December in 2014 were collected, and high-fluorescent cells were counted with Sysmex XE-5000 blood cell analyzer, and then stained for microscopy. Receiver operating characteristic (ROC) curve was used to explore the sensitivity, speci-ficity, positive likelihood ratio and negative likelihood ratio of high-fluorescent cell for screening malignant hydrothorax or ascites. The numbers of high-fluorescent cells of the cancer patients were significantly higher than those of the non-cancer patients, with Z equal to -7.372 and P less than 0.05. The values of the area under curve (AUC), sensitivity, specificity, positive likelihood ratio and negative likelihood ratio were 0.801, 70.67%, 84.31%, 4.50 and 0.35 respective-ly. Detection of high-fluorescent may be used to screen malignant hydrothorax or ascites, and further exami-nation and follow-up have to be performed in case the number of high-fluorescent cells in the hydrothorax or ascites is not less than 68.