Nitrite　accumulation　was　always　observed　in　the　saline　wastewater　nitrification　process,　but　the　effect　of　NaCl　salinity　on　ammonia-oxidizing　bacteria　(AOB)　activity　and　kinetic　characterization　has　not　been　clear.　In　this　study,　AOB　was　enriched　in　a　lab-scale　SBR　system　with　high　concentration　of　ammonium　wastewater,　and　the　partial　nitrification　was　successfully　achieved.　The　fluorescence　in　situ　hybridization　(FISH)　analysis　showed　that　AOB　accounted　for　(55±7)%　of　total　bacteria.　The　maximum　specific　ammonia　oxidation　rate　was　(0.92±0.13)　gN/(gVSS·d).　The　effect　of　NaCl　salinity　on　AOB　activity　was　investigated　using　this　mixed　culture.　The　kinetic　parameters　of　AOB　(KNH3,　Ko)　were　also　measured　under　NaCl　salinity　of　10　g/L.　Results　showed　that　compared　with　NaCl　salinity　0　g/L,　the　activity　of　AOB　decreased　37%　under　NaCl　salinity　of　15　g/L　and　decreased　85%　under　NaCl　salinity　of　30　g/L.　When　salinity　was　10　g/L,　the　maximum　ammonia　oxidation　rate　was　(0.62±0.03)　gN(gVSS·d),　the　half-saturation　constant　for　ammonia　(KNH3)　was　(7.62±0.13)　mg/L,　the　half-saturation　constant　for　oxygen　(Ko)　was　(0.39±0.04)mg/L.　The　KNH3　value　was　higher　than　recommended　value　of　ASM2　model.　NaCl　salinity　could　reduce　maximum　specific　ammonia　oxidation　rate,　and　also　affects　the　substrate　(ammonia)　affinity　of　AOB.　©,　2015,　Chinese　Society　for　Environmental　Sciences.　All　right　reserved.