The synthesis of oleic acid phytosterol esters catalyzed by Zr(SO4)2·4H2O under free medium was investigated. The reaction conditions were optimized using response surface methods (RSM) measured by the degree of esterification (DE). A quadratic response regression equation of esterification rate on independent variables of temperature, substrate molar ratio (oleic acid: phytosterol), reaction time and catalyst amount was established. Under the optimized reaction conditions, the DE of phytosterol with oleic acid reached 93% and then the phytosterol esters catalyzed in the optimum condition confirmed by the GC and FTIR analysis. It was concluded that the esterification of phytosterols and oleic acid by the green catalyst Zr(SO4)2·4H2O is very efficient and this supplied as an alternative to the green synthesis of phytosterol esters.