To improve the nitrification efficiency of activated sludge in a low temperature (15 ℃） sequencing batch reactor (SBR), the performance and characteristics in nitrification of the activated sludge were investigated by batch culture with regulation of initial pH. The results indicated that the ammonia oxidation efficiency of the activated sludge was the best with initial pH ranged from 8.0 to 9.0. In the NO₂--N accumulating process, the specific ammonia nitrogen (NH₄+-N) removal rate and specific nitrite nitrogen (NO₂--N) producing rate were 25.49 g·kg-1·d-1 and 22 g·kg-1·d-1(as MLSS), respectively. For nitrite oxidation, the favorable initial pH ranged from 7.5 to 8.0, under which a specific nitrate nitrogen (NO₃--N) producing rate of 35.6 g·kg-1·d-1(as MLSS) was obtained. It showed that the satisfactory ammonia oxidation and nitrite oxidation efficiency would be obtained by the enhancement of metabolic activity both of the nitrite and nitrate bacteria when the pH of wastewater was kept at about 8.0 in the nitrification process.