Factors affecting on dewatering characteristics of anaerobically digested or/and elutriated sludges were examined from 15 January 1982 to 30 April 1982, results obtained were as follows 1. Sludges, either anaerobically digested or/and elutriated sludges, which were produced at the Joong Rang Cheon Sewage Treatment Plant wore found to be compressive in its nature, coefficient of compressibility ranged from 0.83 for unelutriated and 1.10 for elutriated. 2. Dosage of FeC13 for the anaerobically digested sludges were difficult to establish for the most favorable dosage rate, though the filterability indicated linear improvement with increased dosage from dosing rate excess of over 15% in terms of dry solids by weight, under the conditions of this examination. Optimum filterability were obtained with 9~11% of $FeCl_3$ for elutriated sludges, and required CaO, as aids, were appeared to be 2.5~3.5 times that of the $FeCl_3$ at that point by weight. 3. The specific resistances for anaerobically digested sludges showed higher value than the elutriated one, being $11 imes 10^{12} ~ 20 imes 10^{12}$ cm/g with no chemical conditioning, and $2 imes 10^{12} ~ 11 imes 10^{12}$ cm/g with conditioned ($FeCl_3$ + CaO) contrast to $0.5 imes 10^{12} ~ 2.0 imes 10cm/g$ for the elutriated. 4. The strength of the alkalinities before and after elutriation were measured to 10,000 ~ 15,000 mg/l and 1,500 ~ 2,000mg/l respectively. These alkalinities affected greatly on the filterabilities together with concentration of the organic matters in the sludges. 5. The yields with 11% $FeCl_3$, by weight to the DS, on the elutriated sludges averaged to $14.7 kg/m^2.hr$, and $3.2kg/m^2.hr$ for unelutriated sludges. Which was 4.6 times of not elutriated sludges. Elutriated sludges without chemical conditioner added showed much better filterabilities than with 15% of $FeCl_3$ added to the anaerobically digested and unelutriated sludges.