Bakery yeast is a valuable material for the production of bread, which increases food value, flavor and volume of beard. One of the most problems in the production of bakery yeast is ouput wastewater from the manufacturing unit which releases much pollution to the environment. Membrane bioreactor (MBR) technology is one of the newest methods in municipal and industrial wastewater treatment and generally replaces the conventional treatment methods. This technology is a combination of the biological process and membrane separation process which is used commercially and industrially in advanced and developing countries. Advantages of MBR technology are the high quality of the output stream, less required space; quick installation and so on. The objective of this research is evaluation of treatment of bakery yeast factory wastewater by membrane bioreactor technology. Experimental setup was designed and constructed according to various studies in the field of industrial wastewater treatment. Hollow fiber membrane modules of dead-end immersed type with pore size of 0.26 µm was used in bioreactor. In the biological process, Aspergillus oryzae microorganism was prepared and inoculated for biochemical reactions. This microorganism was adapted with wastewater in the bioreactor for two weeks. After microorganisms being adapted, the physical and chemical tests such as chemical oxygen demand (COD), biochemical oxygen demand 5-days (BOD 5 ) and suspended solids of concentrations and turbidity were measuring in the feed inlet and permeate of membrane during the operation. Mixed liquor suspended solids concentration was in the range of 4100 to 9100 mg/L in membrane bioreactor system. The theoretical hydraulic retention time of 22 h was considered in this research. Membrane critical flux was obtained 6.7 L/ m 2 .h by Flux-Step method which based on operation flux was considered 5 L/ m 2 .h in membrane bioreactor. By calculating three types of affecting resistance on membrane performance using permeate flux and trans membrane pressure, which basis of these values the total membrane resistance was obtained 8.333×10 12 m -1 . In this research, the average organic loading rate of 4.2 kg COD/ m 3 .d was enter to the bioreactor and outlet COD and BOD 5 were reduced to 488 and 70 mg/L, respectively during operating time of 45 days. The highest COD and BOD 5 removal efficiency in the MBR process were obtained 82.2 and 88.0 %, respectively. This method of wastewater treatment reduced the turbidity from between 134 and 282 NTU in feed to less than 2.5 NTU in permeate stream. Permeate pump was operated with a mode of 5.5 min on and 30 sec off during the operation in order to reduce the fouling rate in membrane module. The membrane was washed by distilled water to remove the fouling and permeate flux recovery. In the case of excessive fouling, the sodium hypochlorite solution was used for washing. Keywords : membrane bioreactor, bakery yeast, wastewater treatment, hollow fiber membrane, membrane fouling