A novel biofilm reactor named as 'rotating perforated tubes biofilm reactor (RPT)' was developed and used for biological treatment of synthetic wastewater. Effects of major process variables such as COD loading rate, specific biofilm surface area, number of tubes and the rotational speed (rpm) on COD removal performance of the reactor was investigated. COD removal efficiency increased with the specific biofilm surface area and the rotational speed, but decreased with increasing COD loading rate. Kinetics of COD removal was investigated and kinetic constants were determined by using the experimental data. An empirical design equation was developed to quantify the system's performance as a function of the operating variables.