There are a lot of parameters affecting microbial acclimation/cultivation characteristics such as dynamic conditions, F/M ratio and substrate affinity. From the process control point of view, the effect of high salinity on the removal efficiencies of BOD and SS have been documented by few researchers. In this research, lab-scale CAS(Conventional Activated Sludge) process and modified A2O(Anaerobic/Anoxic/Oxic) process were operated and monitored to evaluate the characteristics of microbial acclimation and cultivation under high salinity wastewater during the period of three weeks. As a result of acute microbial activity test(6hr) at various Clconcentration, the appropriate Cl- concentration for microbial growth and acclimation ranged under 3,100 mg/ℓ. As a result of acclimation/cultivation test, the trend of COD removal efficiency reduced gradually as time elapsed. It is considered that NH4-N removal phenomenon of the conventional pollutants removal mechanisms gave little effect to the microbial acclimation/cultivation under high salinity wastewater.