Abstract: Ammonia oxidizing bacteria were screened and isolated from aquaculture water， sludge and rural rivers. Following characterization of the phylogeny of the isolated strains based on their denitrifying capability， the effects of carbon source， C/N ratio， initial pH， inoculation quantity， rotation speed and temperature on ammoxidation characteristics were studied. It was shown that 30 ammonia oxidation strains were obtained by screening on plates of ammoxidation medium. One strain named AOZ1 exhibited the highest ammoxidating capability， and was designated as Enterobacter sp based on 16S rDNA sequence and phylogenetic analysis. The optimum condition for ammoxidation was as follows: sodium acetate as carbon source， C/N ratio 15∶1， inoculation amount 1%， initial pH 7.5， rotational speed 200 r·min-1， and temperature 30℃. Under this condition， the removal rate of ammonia nitrogen reached 98.70%.

Key words: ammoxidation, screening, characteristics, Enterobacter sp.