This study was carried out to investigate the effects of operating temperatures on decomposition and physicho-chemical properties of household food wastes in a fermentation dryer, which was manufactured by Samwoo Co. Ltd. The household food wastes of 100 kg can be put and dried in this dryer at once. The experiments were perfumed at each temperature of 35℃, 45℃, 55℃ and 70℃ for two days respectively and the samples taken at the fixed time were dried at 105 ℃ and analyzed to find the decomposition rate and the concentration of each substance. The results obtained were as follows : The decomposition rate at 35 and 70 ℃ was the highest and showed the similar tendency during the experimental period. The higher the operating temperature was, the faster the water content of the composting material reduced. pH value increased at the operating temperature of 55 and 70 ℃ and was higher than at the other operating temperatures. Nitrogen content did not show any tendency during the experimental period. P₂O₅ and CaO content increased during the experimental period but MgO, K₂O and NaCl were not accumulated. Cu content was less than the by-product compost limit value and Cd, Pb and Cr were not detected.