Abstract: Objective:To detect the level of acetaldehyde dehydrogenase 1(ALDH1) of ascites,and explore the value and significance of ALDH1 in differential diagnosis of benign and malignant ascites.Methods:The levels of ALDH1 in 32 malignant ascites cases and 22 benign ascites cases were detected using ELISA.The levels of ALDH1 in benign and malignant ascites,and different primary diseases were analyzed.Results:The age in malignant ascites group was higher than that in benign ascites group(P<0.05),but the difference of the gender distribution between two groups was not statistically significant(P>0.05).The differences of the levels of ALDH1 in two groups among different ages and genders were not statistically significant(P>0.05).The levels of ALDH1 in malignant ascites group was significantly higher than that in benign ascites group(P<0.05).Among few primary tumors,the level of ALDH1 in malignant ascites of liver cancer was the highest,and the differences of the levels of ALDH1 amony digestive tract cancer,endometrial cancer,ovarian cancer and pancreatic cancer were not statistically significant(P>0.05).Among the benign ascites,the level of ALDH1 in liver cirrhosis ascites significantly increased compared with tuberculous peritonitis ascites(P<0.05).Conclusions:ALDH1 has important significance in the differential diagnosis of benign and malignant ascites,and identifying the primary disease of ascites.