The most dominant and beneficial conjugated linoleic acids isomers (CLAs) with miscellaneous biological tasks are 9c11t-C18:2 and 10t12c-C18:2. The problem with most of the commercial CLA produced by non-optimized conventional approaches is the heterogeneity of their isomers and undesirable toxic by-products. In this study, optimization of the isomerization of the fatty acid methyl esters of the high linoleic sunflower oil was investigated through response surface methodology (RSM). The reaction temperature, the concentration of PEG400 and NaOCH 3 had positive influence on the total conjugated linoleic acid methyl esters (CLAME) production as response. However, the effect of the polyethylene glycol 400 (PEG400) concentration was more significant on response than those of other factors (p < 0.05). The reaction time and the interactions between the factors had no significant effect on response (p ≥ 0.05). The optimum point for the maximum response of 72.90% (i.e., based on the mass percentage of total fatty acid methyl esters mixture) was at 5% w/w NaOCH 3 , 1.06% w/w PEG400 and temperature of 140˚C.