In this research, new coagulant was synthesized by copolymer reaction using starch and acrylamide. The compositions of testing materials were SCSA30(starch 30%, acrylamide 70%), SCSA40(starch 40%, acrylamide 60%) and SCSA60(starch 60%, acrylamide 40%). Then, coagulation tests under proper pH condition were conducted for sample obtained from a mixing control tank of nightsoil treatment plant in Na-ju City. Concentrations of coagulant prepared for the tests were w_t. 2%, w_t. 4% and w_t. 6%. Optimum dosages were determined sludge. 1. It is concluded that pH 7.0 was optimum condition for the test using w_t. 2% of SCSA30. 2. The best coagulation reaction in terms of suspended solid concentration showing 32㎎/L was obtained when w_t. 4% of SCSA30 was used. 3. In terms of effluent concentrations for the BOD_5, COD_(Cr), TKN and water content w-1. 4% of SCSA30 consistently showed the highest removal efficiency. However, w_t. 2% of SCSA40 was shown to be the best for the treatment of Total Phosphorus. 4. For the test of dehydration ability, the lowest value of specific resistance was obtained where w_t. 4% of SCSA30 was applied. Optimun dosage was turned out to be 50㎖ of coagulant per 1ℓ of sample.