P(AM-ADE), a novel cationic polyelectrolyte, was N-(2-(acryloyloxy)ethyl)-N '-dodecyl-N,N,N ',N '-tetramethyl ethane-1,2-diaminium dibromide (ADE) copolymerized with acrylamide (AM) in inverse emulsion. The performances of activated sludge conditioned with this polyelectrolyte were investigated and evaluated with capillary suction time (CST), settling rate and water content in sludge cake after filtration. The floc morphological parameters (floc size and fractal dimension) and physical properties (sludge viscosity and zeta potential) were also measured. Compared with common conditioners TC-302 and TC-304, the synthesized polyelectrolyte has the properties of lower molecular weight, higher concentrated charge density and hydrophobically associative interaction due to the special structure of functional cationic monomers. The experimental results indicated that sludge conditioned with P(AM-ADE) could retain less water content in filtrated cake and form relatively more compact flocs. Furthermore, a multilayer adsorption and lower molecular weight resulted in less chance of overdosing. However, more dosage was required to obtain the satisfactory flocculation effect when the P(AM-ADE) was used as sludge conditioner.