The dewaterability of a sludge can be characterized by two ways: the residual moisture centent in the sludge cake after dewatering process, and the filteration of the sludge. Time to filter (TTF) and specific resistance to filtration (SRF) represent filtration processes that are special cases of the flow through a solid matrix concept. TTF and SRF characterize a resistance to filtration. The sludge resistance, in turm, can be subdivided into resistances associated with the solid phase and the liquid phase, to evaluate the effect of each of the two phases on sludge dewaterability. The results showed that cationic polymers were more effective than anionic polymers in the dewatering characteristics of the waterworks sludge. Polymer (C-7650) was chosen for dewatering experiments of waterworks sludge. A correlation coefficient value(0.9925, n=18) between TTF and SRF was very high. As the cake solids concentration increased from 0.12 to 1.23%, the optimal dose of the polymer increased from 1 to 30 ㎎/l.