Abstract: The amount of heterotrophic bacteria and metabolic activities of microbial communities in the sediment of Tilapia culture ponds were investigated by using plate count method and Biolog ECO microplate. The results showed that the amount of heterotrophic bacteria in the sediment was stable in the whole farming period, ranging between (8.4±5.7)*1000000 and (5.2±4.2) *10000000 CFU/g and peaking in June, and the differences in metabolic activities and functional diversities of the microbial communities were not significant among each month. The characteristics of carbon metabolism of the microbial communities were also analyzed. The results showed that there was no significant difference among each month in the utilization of four kinds of carbon sources. However, there were significant differences in the utilization of different carbon sources, higher rate was found for the utilization of saccharides, and low rate was found for the utilization of amino acids, fatty acids, metabolic intermediates and secondary metabolites.