Abstract: Objective To track fecal pollution sources in Guiwu reservoirat Xuyu,Jiangsu province with repetitive extragenic palindromic polymerase chain reaction(rep PCR)microbial source tracking method(MST).Methods Fresh fecal samples from human and anmials(poultry,livestock,dogs,and wild animals)were collected in villages around Guwiu reservoir in four seasons in a year.Escherichia coli were isolated and identified by API20E as the indicator.A known source fingerprinting library containing all kinds of anmial and human feces possibly polluting the water of the reservoir was devel oped.Then the library with Bionumerics 4.0 was used to calculate average rate of correct classification.Multivariate analysis of variance(MANOVA)and discrmiinant analysis were also conducted to evaluate the ability of discr imination of the library.Water samples were collected once a month,and Escherichia coli were isolated with membrane filtration and identi fied with API20E.The Escherichia coli wase subject to rep-PCR amplification.The fecal pollution sources were identified statistically by compared the rep-PCR fingerprinting of each Es cherichia coli from water sample with those from the known source library.Results When the known source fingerpr intlibrary was classified as 2,3,4,5 and 9 groups,the average rates of correct classification were 89.19%,77.58%,76.69%,75.25%,and 70.92%,respectively.MAN OVA and discrmiinant analysis showed that the division of different groups was clearly.Five hundred and thirty four indicators from water samples were identified for theirs pollution sources from human(26.49%),chicken(14.74%),duck(7.77%),go ose (5.78%),do g(3.98%),pig(7.97%),cattle(10.96%),go at(8.76%),and wild anmials(8.57%),respectively.Conclusion There sults showed that there are lots of sources of fecal pollution in water of Guiwu reservoir with human,chicken and cattle as the main contributors of the pollution.The MST is a new and useful method for tracking and evaluating the source of fecal pollution in nature water.