Abstract: The effects of eight chemicals,including o-chlorophenol(oCP),m-chlorophenol(mCP),2,4-dichlorophenol(DCP),2,4,5-trichlorophenol(TCP),p-nitrophenol(pNP),m-nitrophenol(mNP),2,4-dinitrophenol(DNP) and 3,3′,4′,5-tetrachlorosalicylanilide(TCS),on sludge yields in batch cultures were compared.It was found that these eignt chemicals are good uncouplers which can effectively reduce sludge yield.Nitrophenol chemicals were better than chlorophenols.The two chemicals DNP and pNP were the most effective uncouplers of activated sludge respiration with control rates of 89.16% and 83.77%,respectively.The metabolic uncoupler with a lower pK_a has a higher potential to reduce sludge production.The sludge yield decreased with the increase of uncoupler mass concentration.When the uncoupler mass concentration was constant,sludge yield increased with the increase of sludge mass concentration.High sludge mass concentration would weaken the effect of uncoupler.Therefore,the specific uncoupler concentration,i.e.the ratio of uncoupler mass concentration to sludge mass concentration was a better criterion to choose uncoupler.