Altlhough ammonia oxidation and ammoniaoxidizing bacteria (AOB) have been extensively studied,nitrite oxidation and nitrite-oxidizing bacteria (NOB) are still not well understood. In this article, the effect of organic matter on NOB and heterotrophic bacteria was investigated with functional performance analysis and bacterial community shift analysis. The results showed that at low concentrations of initial sodium acetate [initial sodium acetate(ISA) = 0.5 or 1 g/L], the nitrite removal rate was higher than that obtained under autotrophic conditions and the bacteria had a single growth phase, whereas at high ISA concentrations (5 or 10 g/L), continuous aerobic nitrification and denitrification occurred in addition to higher nitrite removal rates, and the bacteria had double growth phases.The community structure of total bacteria strikingly varied with the different concentrations of ISA; the dominant populations shifted from autotrophic and oligotrophic bacteria (NOB, and some strains of Bacteroidetes, Alphaproteobacteria,Actinobacteria, and green nonsulfur bacteria)to heterotrophic and denitrifying bacteria (strains of Gammaproteobacteria, especially Pseudomonas stutzeri and P. nitroreducens). The reasons that nitrite removal rate increased with supplement of organic matters were discussed.