In　this　study,　the　short-term　effect　of　roxithromycin　(ROX)　on　the　abundance　and　diversity　of　ammonia-oxidizing　archaea　(AOA)　and　ammonia-oxidizing　bacteria　(AOB)　based　on　amoA　gene　in　activated　sludge　were　investigated　by　high-throughput　sequencing　and　quantitative　real-time　PCR(qPCR).　High-throughput　sequencing　overcomes　the　drawbacks　of　low　sequencing　depth,　significant　randomness　and　great　bias　of　traditional　Sanger　sequencing.　This　approach　can　provide　enough　sequencing　depth　to　comprehensively　investigate　the　sensitive　and　insensitive　ammonia-oxidizing　microorganisms　under　ROX　selective　pressure.　Lab-scale　reactors　were　operated　under　ten　different　ROX　levels.　The　results　indicated　that　the　environmental　(0.3-30　μg·L-1)　and　medium　(300　μg·L-1and　3000　μg·L-1)　levels　of　ROX　did　not　affect　ammonia　oxidation,　while　the　higher　concentration　(5000-12000　μg·L-1)　of　ROX　showed　a　significant　negative　effect　on　ammonia　oxidation.　The　environmental　and　medium　levels　of　ROX　stimulated　the　growth　of　AOA,　however,　the　higher　level　of　ROX　decreased　the　abundance　of　AOA.　In　addition,　different　levels　of　ROX　(except　0.3　μg·L-1)　caused　the　decrease　of　the　abundance　of　AOB,　which　suggested　that　AOA　was　less　sensitive　than　AOB　under　ROX　selective　pressure.　The　results　of　high-throughput　sequencing　showed　that　ROX　selective　pressure　caused　the　decrease　of　the　numbers　of　OTUs　for　AOA　and　increase　of　that　for　AOB.　The　insensitive　AOA,　accounting　for　57.70%-97.81%　of　the　total　sequences,　were　Candidatus　Nitrososphaera　gargensis　and　Candidatus　Nitrosoarchaeum　koreensis.　The　insensitive　AOB　were　Nitrosomonas　oligotropha,　Nitrosospira　multiformis,　Nitrosomonas　watsonii　and　Nitrosomonas　halophilus,　accounting　for　0.76%-5.10%　of　the　total　sequences.　These　results　also　indicated　that　AOA　was　insensitive　to　ROX,　but　AOB　was　sensitive　to　ROX.　RDA　analyses　showed　that　AOA　Ca.　Nitrososphaera　gargensis,　Ca.　Nitrosoarchaeum　koreensis　and　AOB　N.　oligotropha,　N.　watsonii,　N.　halophilus　were　positively　correlated　with　ROX　concentrations.　©　2017,　Science　Press.　All　right　reserved.