In this study, the effect of operational conditions on biofilm development and nitrification in moving-bed biofilm reactor (MBBR) was investigated. The reactor was operated in a continuously fed regime during 170 days and with theoretical hydraulic retention time of 7 h, respectively. The presence of chemical oxygen demand (COD) increased the time required to form stable nitrifying. Subsequent stepwise increase of influent COD caused an increment in total polysaccharide (PS) and protein (PN) content, which was accompanied by an attachment of the biofilm, as shown by atomic force microscope (AFM). PS and PN concentrations proved to be good indicators of biomass development and attachment in MBBR system. Reactor was operated and water quality was characterized before and after treatment. Parameters including pH, 5-day biochemical oxygen demand (BOD5), total suspended solids (TSS) (COD), PN, PS, and fecal bacteria in both raw and treated wastewater were monitored during the treatment. The removal rates of ammonium-nitrogen (NH4 (+)-N), BOD5, COD, and TSS are 95, 67.5, 69.2, and 73.33 %, respectively. The average bacterial reduction between the inlet and the outlet was of the order of 5 +/- A 1 logarithmic units for fecal coliforms. AFM showed that distinct biofilm and extracellular polymeric substances were formed in biofilm was thicker in the 70 days than in the 30 days. These results showed that the consumption rate for each substrate increased parabolically with biofilm thickness due to the increased amount of biomass Thus, MBBR can serve as a promising technology for wastewater treatment and can be scaled up for small communities in the developing countries.