The present continuous studies are undertaken to develop an effective anaerobic digestion process of sugar industry wastewaters for biogas generation using actively digested sludge from a sewage plant in three-phase fluidized bed bioreactor. Attempts are made to optimize hydraulic retention time (HRT), initial feed pH, feed temperature and flow rate of feed (organic loading rate) for maximum yield of methane (CH4) gas and removal of chemical oxygen demand (COD) and biological oxygen demand (BOD) of sugar industry wastewaters. The optimum HRT is 8 h and optimum initial pH of feed is observed as 7.5 respectively. The optimum temperature of feed is 40 °C and optimum feed flow rate is 14 L/min with maximum organic loading rate (OLR) is 39.513 kg COD m-3 h-1 respectively The organic loading rates (OLR) are calculated on the basis of COD inlet in the reactor at different flow rates. The maximum expansion of the bed is observed as 23.67 m at optimum feed flow rate of 14 L/min. The maximum methane (CH4) gas concentration is 63.56% (v/v) of the total biogas generation at optimum bioprocess parameters. The maximum biogas yield rate is 0.835 m3 /kg COD m-3 h-1 with maximum methane gas yield rate of 0.530 m3 /kg COD m-3 h-1 respectively at optimum bioprocess parameters. The maximum COD and BOD remediation of the sugar industry wastewaters are 76.82% (w/w) and 81.65% (w/w) with maximum OLR of 39.513 kg COD m-3 h-1 respectively. The bioprocess parameters are optimized for the scale-up of fluidized-bed bioreactor design to be used in industrial applications. Copyright © 2008 American Scientific Publishers. All rights reserved.