Sodium benzoate has been used a food preservative worldwide. The effect of sodium benzoate as a preservative in the wastewater treatment was examined from the biogas formation. Research was conducted in some batch mode reactor systems employing various ratios of activated sludge and solution of sodium benzoate volume. The MLSS of activated sludge used was 12 g/L, while the volume ratios of activated sludge and sodium benzoate ranged from 0 to 100%. Concentrations of sodium benzoate used were 50, 100, and 200 mg/L. Biogas samples were measured every two days for 60 days. The results showed that the volume ratio of activated sludge and sodium benzoate of 60% and 40% was a turning point where the existence of sodium benzoate influenced the formation of biogas. There were significant reductions of biogas formation from 200.6 mL to 66.6 mL, 159.8 mL to 66.0 mL and 130.2 mL to 54.0 mL for the initial SB concentrations of 50, 100, and 200 mg/L. The kinetic parameters of the Modified Gompertz equation exhibited the greatest degree of confidence of 95%.