Because permeate flux was very low as it has the suspension solid of high concentration in the ultrafiltration membrane separation treatment of dyestuff wastewater, pre-treatment of Fenton reaction was carried out. In the case of pH 3, COD removal rate was the highest of 58%. When PAC was added into the pre-treatment supernatant, the COD removal rate was found to be 53%, and when COD was 153㎎/L, the removal rate was 92.3% in the ultrafiltration separation. In addition, the effect of the addition of PAC on the permeate flux was also investigated. The decrease of permeate flux in the presence of PAC was higher than in the abscence of PAC, but the recovery of permeability by cleaning was better in the case of PAC system.