Response surface methodology coupled with central composite design (CCD) was used to investigate the effects of operating variables, namely, coil outlet temperature (COT), flow rate and steam ratio, on the yield of light olefins (ethylene and propylene) in thermal cracking of heavy liquid hydrocarbon. From the CCD studies the effects of COT and flow rate were concluded to be the key factors influencing the yield of light olefins. Based on this experimental design, two empirical models, representing the dependence of ethylene and propylene yields on operating conditions, were developed. The single maximum response of ethylene and propylene yields and simultaneous maximization of both responses have also been obtained at the corresponding optimal independent variables. The results of the multi-response optimization could be used to find the suitable operating conditions.