This study reports on the fabrication of a novel single chamber microbial fuel cell (MFC) configuration. The single chamber MFC with annular configuration and spiral anode geometry, is suggested for future large-scale applications. There were two main objectives in this study. First, the stainless steel mesh anode with graphite coated as a porous surface for biofilm growing in annular single chamber MFC configuration were designed and its characteristics were investigated. Second, the power generation and internal resistance of the annular MFC with spiral anode geometry was compared to conventional air cathode MFCs to elucidate the effects of this configuration on MFC performance. Dairy wastewater which contains complex organic matter, was used as substrate which has a very low power generation in conventional MFCs. In this study, the maximum power density of 20.2 W/m 3 was obtained. MFC performance as power generator was characterized based on polarization behavior and cell potentials. In addition, significant reduction in wastewater turbidity and chemical oxygen demand (83.5% and 91% respectively) were observed after treatment in the MFC. Effects of varying electrode surface area and dairy wastewater concentration were investigated. With decreasing anode surface area from 2´63 cm to 2´38 cm, output current was reduced about 34%. Also, the MFC with the smaller anode surface area has a much longer stationary phase than that with the larger anode surface area and stationary phase period is increased from 23 hours to 67 hours. Anode geometry and its configuration in the MFC affect specific area and electrodes spacing. The higher specific area and lower space with cathode increase MFC efficiency. Clearly, with reducing anode surface area, biofilm development decelerated compared to greater anode surface area. This led to reduction of substrate degradation. Moreover, by decreasing anode surface area in spiral geometry, electrode spacing is increased that led to increase in internal resistance of the cell. By increasing MFC resistance including external and internal resistances, the duration of stationary phase increased. The wastewater concentration is an important parameter on MFCs performance. By reduction of initial dairy wastewater COD which was fed to annular single chamber MFC from 1000 to 500 mg/lit, maximum output current was decreased from 1.89 to 1.2 mA. In addition, the MFC which was fed with wastewater with COD 500 mg/lit had a shorter descending phase than that of the higher wastewater COD. Moreover, the output current from the MFC fed with dairy wastewater with less COD, reached 0.17 mA after 49 hours while the period of current reduction for the MFC fed with dairy wastewater with higher COD is longer than 72 hours. With decreasing dairy wastewater concentration, output current is reduced due to reduction of organic contents in the anolyte. The SEM pictures of stainless steel mesh with graphite coating before and after biofilm formation, demonstrated a good bacterial adhesion on the spiral anode. Due to the high surface area, large amount of biomass attached to treated stainless steel mesh. Therefore, the porosity of anode can be a suitable place for biofilm formation. Morphology of biofilm was uniform, which facilitated the electron generation and transfer. Keywords: Single chamber microbial fuel cell, effective parameters, annular configuration,spiral anode geometry, dairy wastewater.