Biological processes of wastewater treatmnent have found wide applications due to their lower costs and higher efficiency. Membrane bioreactors (MBR’s) form one group of such processes in which membrane fouling is of great importance. Efficiency of critical flux (CF) has been proved to be a parameter effective in fouling control (CF). CF is itself influenced by three main groups of variables that include sludge parameters, operating conditions, and membrane types. In this stidy, the effects of such factors as trans-membrane pressure, protein and carbohydrate concentrations in extracellular polymeric substances (EPS), and soluble microbial products (SMP) on CF were investigated in a submerged MBR.  Moreover, the effects of such operating conditions as periodic and continuous suctions at two sludge concentrations were studied. It was found that increasing flux led to enhanced membrane fouling rates. Extracellular polymeric substances (EPS) were found to have no relations with critical flux (CF), probably because EPS are mostly found as bigger flocks. Finally, a reverse relationship was established between CF and carbohydrate concentration of the SMP. Membrane fouling control was observed to be positively affected by the rest modes during periodic suctions.