An amphoteric polymer, poly(acrylamide-acryloyloxyethyl trimethyl ammonium chloride-2-acrylamido-2-methylpropane sulfonate) (PADA) was developed for use as a sludge flocculant. It was synthesized in aqueous solution by ternary free radical copolymerization from acrylamide (AM), acryloyloxyethyl trimethyl ammonium chloride (DAC) and 2-acrylamido-2-methyl-propane sulfonate (AMPS) in redox/azo initiation. Single factor experiments and response surface methodology (RSM) were conducted to determine the optimum range of reaction variables and investigate their interactions affecting flocculation capacity of PADA. The minimum predicted response values of specific resistance to filtration (SRF) and content of water(CW) under the optimum conditions were 2.29 x 10(13) m/kg and 77.65%, respectively. In order to observe structural characteristics of polymer, Fourier-transform infrared spectroscopy (FTIR), H-1 nuclear magnetic resonance (H-1 NMR) and Thermogravimetric analysis (TGA) were used. Subsequently, the flocculation characteristics of PADA were proposed systemically by contrastive analysis of the polymer morphology, charge effects and floc characterization with control samples to indicate that amphoteric properties of PADA took positive effects on the sludge flocculation. Finally, treatment of sludge confirmed that PADA was a highly efficient flocculant, which was applicable to be used in a wider range conditions. (C) 2015 Society of Plastics Engineers