<p>A full-scale biofilm system using fluidized-carriers integrated with anaerobic-anoxic&#8211;aerobic process (treatment capacity of 3.75 &#215; 10<sup>5</sup> m<sup>3</sup> d<sup>&#8722;1</sup>) was used for municipal wastewater treatment. The results indicated relatively higher removal efficiencies of 86% total nitrogen (TN), 97% ammonium (NH<sub>4</sub>-N) and 97% total phosphorus (TP) were achieved, with 0.32 mg L<sup>&#8722;1</sup> TP, 0.81 mg L<sup>&#8722;1</sup> NH<sub>4</sub>-N and 8.07 mg L<sup>&#8722;1</sup> TN in the effluent, which meet the Class A of Discharge standard of pollutants for municipal wastewater treatment plant (GB18918-2002) of China. The results of microbial analysis indicated that the dominant microorganisms in the suspended sludge were Proteobacteria and Bacteroidetes at phylum level and &#946;-Proteobacter at class level. The dominant microorganism in the biofilm was Proteobacteria at phylum level, with &#947;-Proteobacter (17.5%), &#946;-Proteobacter (14%) and &#948;-Proteobacter (13.08%) distributed at class levels. The presence of Proteobacteria and Bacteroidetes in this system may be related with the phosphorus removal. A reddish color biofilm was formed on the surface of fluidized-carriers in the anaerobic tank and showed specific anammox ability, this may be related with the dominance of 0.0278% Planctomycetaceae at family level and 0.0278% Planctomycetales at order level. Besides the denitrification effects, the possible anammox bacteria present in the anaerobic tank might have also contributed to high nitrogen removal efficiency.</p>