A system of the oxygen activated sludge process followed by the coagulation process was studied aiming at improving the treatment efficiency for the dyeing industrial complex wastewater mainly containing polyester weight reduction waste. Treating the wastewater in F/M range 0.34∼0.95㎏ BOD/㎏ MLVSS ·day and 0.14∼0.46㎏ COD_(Mn)/㎏ MLVSS ·day with the oxygen activated sludge process, it was found that the specific substrate removal rates were 0.33∼0.93㎏ BOD/㎏ MLVSS ·day and 0.1∼0.38㎏ COD_(Mn)/㎏ MLVSS · day, and the removal efficiency were 98% BOD and 77% COD_(Mn), respectively. The biomass yield coefficient(Y) and the microbial decay coefficient(Kd) were 0.40㎏ MLVSS/㎏ BOD and 0.13 day^(-1). The reactor temperature significantly effects the treatment efficiency. The filamentous microorganism, which was predominant species above 40, has resulted in the deterioration of water quality. It was confirmed that terephthalic acid remaining after the oxygen activated sludge process could be removed by the coagulation with alum at pH 5.