This study investigates the effect of cationic polyelectrolytes oil the final properties of synthetic and activated sludge. Synthetic sludge was prepared according to established procedures. Activated Sludge was produced ill a labscale, continuous-flow reactor which was fed with live activated sludge from a waste-water treatment plant. Capillary suction time (CST) was used to evaluate the Sludge dewatering behaviour. The results from experiments indicated that the cationic polyelectrolytes had a critical effect oil sludge dewatering, and made an improvement in the final properties of sludge. The two types Of Sludge have very similar dewatering characteristics after cationic polymer conditioning. The development of synthetic Sludge is Suggested also to be a possible surrogate for studying the final properties of activated sludge.