Abstract: The bio-activity of activated sludge in the moving-bed biofilm reactor was investigated using oxygen uptake rate (R_ ou ) as an indicator. The R_ ou of both attached-and suspended-growth sludge was determined under different temperature and loading rates. The experimental results indicated that at the temperature of 5 ℃, the nitrification activity was about 60% of that at 18 ℃. The nitrification activity of attached sludge was 20%～30% lower in comparison with suspended sludge. The bio-activity of suspended-and attached-sludge in two reaction zones was in following order: suspended-Ⅱ>suspended-Ⅰ>attached-Ⅱ>attached-Ⅰ. The denitrification rate of sludge in zone Ⅰ and zone Ⅱ was 0.44 and 0.63 mg/(g·h), respectively, which revealed that the denitrification activity of sludge-Ⅱ was higher compared with sludge-Ⅰ, the results also indicated that the accumulation of nitrite was very low.