In situ identification of ANAMMOX bacteria was conducted using 16S rRNA approach for sediment samples from the Xinyi River in Jiangsu Province, China. 16S rRNA clone library including 6 clone sequences was constructed. The alignment of these sequences and treeing were conducted using ARB package. Results show that the sediment samples contained 16S rRNA genes closely related to the known ANAMMOX bacterium Candidatus "Brocadia anammoxidans" (similarity of 91%). They also contained 16S rRNA gene sequences from a new branch of Planctomycetes distantly related to the ANAMMOX sequence cluster. However, the microbiological characteristics of these Planctomycetes are to be studied in the future. The detection of ANAMMOX bacteria will lead to further research on ANAMMOX process in the remediation and restoration of freshwater aquatic ecosystems and new understanding of the nitrogen cycle.