Pyrolytic oil from the pyrolysis process of municipal wastewater sludge is a low grade oil which is high in moisture content and viscosity, and relatively low in calorific value. The oil upgrading experiment was performed in this study to upgrade the quality of the pyrolytic oil. The role of the catalyst, and the effect of reaction temperature, WHSV(Weight Hourly Space Velocity) and oil feed rate on the oil upgrading process were evaluated using a bench scale micro reactor. The ZSM-5 catalyzed the upgrading reaction of the pyrolytic oil and simple heating without catalyst did not upgrade the quality of the pyrolytic oil. The viscosity of the oil appears to be dictated not only by the COOH content but also by the other unknown compounds. The O content, moisture content, viscosity, and COOH/CH₃ ratio of the upgraded oil was decreased by 60, 37, 68 and 17%, and the calorific value was increased by 21%, over the feed oil, when ZSM-5 was used in the upgrading reaction.