For this study a ¹⁵N isotope culture was prepared in sediments collected from two eutrophic lakes to determine the potential for the anammox process and denitrification of the sediments. Test result showed that the average reaction rate of the anammox process for the entire year is 137±77 μmol N·m^-2·h^-1, contributing 10.4% to nitrogen gas evolution from the sediments. The anammox process in the lake has an obvious seasonal affect in the following order: summer (237±83 μmol N·m^-2·h^-1) > autumn (133±30 μmol N·m^-2·h^-1) > spring (90±24 μmol N·m^-2·h^-1) > winter (87±26 μmol N·m^-2·h^-1). A positive correlation (P<0.01) exists between the rates of the anammox process and denitrification.