Abstract: The objective of this study is to isolate a strain of heterotrophic nitrification bacterium with high efficiency of removing ammonia-nitrogen from Jialu River of collecting wastewater at Zhengzhou City of Henan Province，and to study its growth characteristics. The collected samples were screened by the traditional methods of microorganism separation and purification，the strain was identified using molecular biology methods，and the culture conditions of the strain were optimized by single factor experiment. Based on 16S rDNA sequence analysis，it was identified as Pseudoxanthomonas sp.，designated as C2. The strain C2 had heterotrophic nitrification and grew rapidly while organic substances existed. C2 entered the logarithmic phase after 4 hours of culturing when the inoculation quantity was 10%. The optimal condition for heterotrophic nitrification was as follows：the inoculation quantity was 3%，the sodium succinate was taken as the only carbon source，the initial pH was 6-9，and the incubation temperature ranged from 25-30℃；the shaking speed had little effect on the activity of removing ammonia-nitrogen in this experiment. In conclusion，the removal rate of ammonia-nitrogen is relatively high，which demonstrates that it is promising to be applied in removing ammonia-nitrogen from practical water bodies.

Key words: heterotrophic nitrification, screening, ammonia-nitrogen, removal efficiency