The detrimental environmental impacts of fossil fuels are increasing due to the growing global energy consumption. Thus, energy recovery from waste will inevitably become the dominant option in the future with population growth and the reduction in fossil resources. In this study; the synthesis gas composition obtained by gasification of biomass attained from a mixture of carbon black obtained from waste tires and sewage sludge originating from the yarn industry was modeled by the response surface method and optimized using Box-Behnken design. The R-2 values obtained for H-2, CO, CH4, and the heating value that make up the synthesis gas composition are 92.86%, 95.40%, 96.15%, and 96.80%, respectively. These are the indicators that the models were statistically significant. Optimum conditions obtained from the model were as follows; reaction time 31.14 min, gas flow rate 0.05 L/minute, and biomass amount 19.66 g. As a result of the validation experiments conducted under optimum conditions, the percentages of H-2, CH4, CO were found as 12.75%, 8.07%, and 7.87%, respectively, and the heating value was 1420.3 kcal/m(3). In conclusion, the gasification process is an appropriate treatment for obtaining high-quality syngas from waste materials with high carbon and low moisture content and the Box-Behnken design is applicable for the optimization of the gasification process.