The changes in the characteristics of nitrosation biofilm were compared in two long-running moving-bed biofilm reactors (MBBR) with two different aeration modes, i.e. continuous aeration and intermittent aeration regimes. The results showed that both continuous aeration and intermittent aeration could achieve the stable growth of the nitrosation biofilm(K_d>0). When with the intermittent aeration regime, continuous biofilm detachment had no effects on the total biomass, and the biofilm growth was more stable. The biofilm under intermittent aeration could obtain a higher total biomass (1.42g/m²) when the MBBR reactor operation was stable. While with the continuous aeration regime, the biofilm could obtain higher PN/PS (1.8~2.0) and PN/VS (0.145), and lower HS/VS (0.05) and the percentage of dead cell (13.66%). This indicated that the biofilm under continuous aeration had a higher proportion of active biomass and living cells, a lower inert biomass, so the biofilm activity was higher and microbial metabolism was more active. The q-PCR results further confirmed that the amount of ammonia-oxidizing bacteria (AOB) was much higher in the biofilm with the intermittent aeration regime than that with the continuous aeration regime. It seemed that the continuous aeration was more beneficial to the AOB growth than that of the intermittent aeration regime in the MBBR (2.36copies×10⁸/g > 0.25copies×10⁸/g).