Abstract: Objective To investigate changes in endotoxin and microbiological parameters after conventional drinking water treatment in main drinking water plants in Wuhan city and to provide a scientific basis for improvement of drinking water quality.Methods The water samples were collected in August 2013 from drinking water plant Z and B with source water from Yangze River and Hanjiang River.The level of endotoxin was determined with limulus amebocyte lysate test described in Chinese Pharmaeopoeia(2005 edition); standard plate-count bacteria,total coliforms,Escherichia coli,and thermotolerant coliform bacteria were detected according to GB/T5750.12-2006 "Standard Examination Methods for Drinking Water-Microbiological Parameters".Results The endotoxin content in raw water samples from drinking water plant Z and B were 281.36 endotoxin unit per ml(EU/ml) and 216.32 EU/ml and that in tap water samples were 38.95 EU/ml and 29.37EU/ml,with the endotoxin removal rates of 86.16% and 86.42% for the two plants,respectively.The value of standard plate-count bacteria for the raw water samples from drinking water plant Z and B were 4.24×10⁴ colony-forming unit(CFU)/ml and 2.06×10⁴ CFU/ml.The content of total coliforms in raw water samples from the two plants were all over 2 300 most probable number(MPN)/100 ml.The content of Escherichia coli and thermotolerant coliform bacteria were 266 MPN/100 ml and 345 MPN/100 ml for raw water samples from plant Z and 1 100 MPN/100 ml and 1 700 MPN/100 ml for the samples from plant B.The standard plate-count bacteria,total coliforms,Escherichia coli,and thermotolerant coliform bacteria were not detected for all tap water samples from the two plants.Conclusion The conventional drinking water treatment can meet the requirement of domestic standard for indicator bacteria,but endotoxin still exists in the output drinking water.