The nitrifying biofilm was formed on the carriers of granular activated carbon with the diameter of 0.613 mm in the airlift bioreactor of 27.7 L to investigate the influences of temperature and dissolved oxygen concentration on the nitrification rate. The biofilm of 0.140 mm thickness was obtained after the operation of 130 days with the dilution rate higher than the maximum specific growth rate of nitrifying bacteria. As raising alternately air velocity and ammonium loading rate, ammonium oxidation rate increased stepwise up to the maximum value of 5 kg N/m(3)ㆍd at the riser air velocity of 6.34 cm/s and the temperature of 30 ℃. The ammonium oxidation rate increased with increasing the dissolved oxygen concentrations, while the nitrite oxidation rates were almost independent from the dissolved oxygen concentration during the early stages of the reactor operation. The biofilm formed at the late phase, however, led the nitrite build-up to disappear and exhibited the nitrite oxidation rates which increased with the dissolved oxygen concentration. As raising temperature, the nitrification rate increased appreciably at the low temperatures of 5 ℃ to 20 ℃ and then slightly at the high temperatures of 20 ℃ to 30 ℃. The oxygen diffusion in the biofilm played a dominant role at high temperatures rather than the nitrification kinetics.