The preliminary enrichment of anammox (anaerobic ammonium oxidation) bacteria from sludge of UASB system treating swine wastewater in Ho Chi Minh city was successfully carried out. Data from 9 months of continuous enrichment showed the simultaneous consumption of ammonium and nitrite (0-81.5 percent and 0-85.6 percent of influent concentration, respectively) and the production of small amount of nitrate (1.0-1.5 mg/l), which meant anammox reaction had occurred. Analysis of enriched biomass by PCR and 16S rDNA sequencing techniques confirmed the existence of anammox bacteria with the high similarity with KOLL2a and KU2 stra.ins and Candidatus Brocadia anammoxidans bacteria, all of which are well known as microorganisms having anammox activity.