An investigation was done on the process kinetics of a two-stage (modified septic tank plus anaerobic filter) anaerobic bioreactor while treating actual domestic wastewater. The individual values of second-order substrate removal rate constant (k) for septic tank and anaerobic filter were observed as 0.36 and 0.26 per day, respectively. It was 0.49 for the combined system. The maximum removal rate constant (U-max) and saturation value constant (K-S) were 737 and 934 mg/L/d, respectively, for anaerobic filter when the modified Stover-Kincannon model was applied to this part of system. Both the second-order and the modified Stover-Kincannon models exhibited high correlation coefficents (R-2 = 98-99%).