Recently, among the immobilized microorganisms technologies, the self-immobilization method is drawing particular attention because it requires neither carriers nor chemicals like the other methods. Although this self-immobilization of activated sludge is thought to be rather new concept, it has been already put to practical use in the methane fermentation as the Unaerobic Upflow Sludge Blanket (UASB) process. However, Aerobic Upflow Sludge Blanket(AUSB) process is a new biological wastwater treatment method applying the concept of the self-immobilization to aerobic activated sludge. In the AUSB process, aeration and biological reaction happen independently in seaprate devices, with the result that the sludge itself is not aerated. And the reactor is designed as an upflow type, in which the biological reaction and solid separation are accomplished simultaneously. Because of this, the final settling tank can be excluded. This research is concerned with the operation of AUSB reactors for synthetic wastewater treatment. Thus, the objectives of this research are to form granules, increase the population of the microorganisms in the bioreactor and find out the optimized initial operating condition for granulation. In this experiment the formation of granules was observed approximately four days after the start of the experiment. The granules were 0.5-2.5mm in diameter and mainly consisted of bacteria with pili-like appendages and filamentous bacteria, which were thought to be Sphaerotilus natans and Begiatoa. Ciliata consisted of Vorticella were common on the outer surface parts of granular sludge. Granulation process seemed to be controlled by physical stress and packed media in upper parts of reactor during the start-up. Under the condition of 2.25kg/㎥·day of BOD volumetric loading, BOD removal efficiencies were over the 90% and average effluent BOD and SS are 22.4mg/l and 16mg/l respectively.