In the present paper an attempt has been made to establish the non-linear input-output relationships to model mechanical properties of structural steel with the help of Response Surface Methodology. Central composite design is utilized to conduct the experiments. Further, surface plots have been developed for response namely Yield strength, Ultimate tensile strength and Elongation. The experiments have been conducted as per central composite design where all process variables are set at three levels. The surface plots showed that alloying elements Manganese, Silicon and Carbon have positive contribution towards both responses Ultimate tensile strength and Yield strength. Moreover, analysis of variance test has been conducted to determine the statistical adequacies of the developed models. The alloying elements Carbon and Manganese showed more contribution as compared to Silicon. It is to be noted that all the three alloying elements are found to have negative contribution towards the response- Elongation. The developed nonlinear regression models for the responses Yield strength, ultimate tensile strength and elongation have been tested for their prediction accuracy with the help of test cases. The present work is found to be useful to control the mechanical properties of structural steel by varying the major alloying elements. Moreover, most of the surface plots have shown a linear relation with the responses.