A membrane module including grid was designed and introduced to MBR (membrane bio-reactor) for the purpose of better control of membrane fouling. It could be anticipated that the grid enhances the shear force of fluid-air mixture into the membrane surface by even-distributing the fluid-air to the membrane module. As MLSS concentration, packing density which is expressed in the ratio of the housing and the cross-sectional area of membrane fibers (A_m/A_t) and air-flow rate were changed, membrane foulings were checked by monitoring fouling resistances. The total fouling resistance (R_c+R_f) without grid installation (i.e., control) was 2.13×10¹² m^-1, whereas it was reduced to 1.69×10¹² m^-1 after the grid was installed. Regardless of the grid installation, the R_c+R_f increased as the packing density increased from 0.09 to 0.28, however, the increment of resistance for the grid installation was less than that of the control. Increase in the air flow rate did not always guarantee the reduction of fouling resistance, indicating that the higher air flow rate can partially de-flocculate the activated sludge flocs, which led to severer membrane fouling. Consequently, installation of grids inside the housing have brought a beneficial effect on membrane fouling and optimum air flow rate is important to keep the membrane lowering fouling.