There is a need to explore environment friendly fuels and its' performance for the internal combustion engine due to growing consumption of fossil fuel which is contributing in increasing the air pollution levels of earth atmosphere. The purpose of the study is to optimize the factors which are responsible for the performance of engine as well as emission analysis in case of cassia tora biodiesel blends in direct injection diesel engine using RSM optimization technique. Four input parameters have been considered for the present analysis which includes engine load, injection timing, injection pressure, and blend percentage to optimize engine's performance and emission characteristics. This study includes all factors having five codded levels. RSM is used to get optimum amalgamation of the above stated factors to optimize output variables (UHC, BTE, and NOx). Hence, cassia tora biodiesel may leads in achieving better environmental performance with improved commercial value. The experimental design used in the study is based on central composite rotating design (CCRD) matrix. The best combination of input parameters is recorded at 15 obTDC injection timing of fuel, 221 bar injection pressure of fuel, 40% mixing of cassia tora with diesel, and 47% engine load which results in maximum BTE and minimum UHC and NOx emissions of the engine. Experimental and optimized results of the output responses at optimum input parameters are compared and found to be in the suggested error range. From the future point of view, same work can be extended by utilizing the same biodiesel with some changes in the input parameters and output responses by utilizing the RSM technique and making its comparison with other techniques. © 2018 Elsevier Ltd