The individual effects and interactive effects of substrate concentration, ratio of inoculum to substrate, Ca2+ concentration on the methane yield from the effluent of bio-hydrogen fermentation of food waste were investigated in this study. A central composite design (CCD) and response methodology (RSM) were employed in designing the experiments, in order to determine the optimum conditions for methane fermentation. The experiment results showed that the effects of substrate concentration, ratio of inoculum to substrate, Ca2+ concentration were statistically significant at 5% level. The interactive effect of substrate concentration and ratio of inoculum to substrate was significant.. however the interactive effect of substrate concentration and Ca2+ concentration, ratio of inoculum to substrate and Ca2+ concentration were found to be insignificant at 5% level. A maximum yield of 565.76 ml CH4/g VSadded was estimated under the optimum conditions for substrate concentration 7.77 g of VS/l, inoculum to substrate ratio of 2.81 and calcium concentration of 380.82 mg/l. Verification experiment of the estimated optimum conditions confirmed that the RSM was useful for optimizing the methane yield from effluent of bio-hydrogen fermentation of food waste. (C) 2007 Elsevier Ltd. All rights reserved.