In this study, some field tests were conducted at ITOB Organized Industrial Zone Wastewater Treatment Plant where membrane bioreactor (MBR) process has been used for wastewater treatment. The MBR treatment process provides stable and high quality product water but product water still contains high salinity in this case. Therefore, a mini-pilot scale membrane test system having three different nanofiltration (NF) which are NF90, NF270 and TR60 and two different reverse osmosis (RO) membranes which are BW30 and AG with spiral wound configurations was employed for demineralization of MBR effluent. The system was operated with 10 bar of operating pressure for NF membranes and at 20 bar for RO membranes. The average water recoveries of NF membranes were 50.2%, 56.0% and 51.8% for NF90, NF270 and TR60 membranes, respectively while average water recoveries of RO membranes were 64.0% for BW30 membrane and 62.3% for AG membrane. The qualities of product waters were analyzed and compared with standards to reuse them for agricultural irrigation and as process water. The permeates of NF270 and TR60 membranes agreed well with the third class water quality for salinity and the second class quality for the rest of parameters. On the other hand, the permeates of NF90, BW30 and AG membranes provided with the first class water for all parameters except for infiltration. Mixing the permeates of NF and RO membranes with MBR effluent in appropriate ratios was considered to be helpful to get acceptable quality values for product water and a good permeability for agricultural irrigation. Therefore, an optimum theoretical mixture of MBR effluent to permeates was determined. When qualities of product water obtained by NF and RO membranes were compared with the standards of cooling and boiling feedwaters for industrial usage and with the process water characteristics for pulp and paper, textile industries, it was considered that the permeates of NF90, BW30 and AG membranes obeyed well the quality standards required.