The study was determining the feasibility of a co-composting process of scum from grease trap and night soil sludge by using window composting process. The composting time, degradation of organic matter and characteristics of compost were evaluated in this study. The scum and night soil sludge were mixed together with C/N ratio at 30:1 and the moisture content was controlled at 40-60% by weight. The study found that the maximum temperature in composting pile was 50.17°C and the optimum composting time was found at 110 days. The concentration of TOC decreases from 44.10% to 34.89% whereas that of FOG decreases from 29.38% to 3.13% by weight. The characteristics of compost with 2.72% of TN, 6.42 of pH level and12.83 of C/N ratio were in the acceptable level compared to compost standard of Thailand. Therefore, co-composting of scum and night soil sludge can be used in scum management.