Limited amounts of fossil fuels and their adverse effects on climate change have prompted scientists to look for alternative energy sources. Biodiesel is proven to be one of the solutions for this problem. Fundamental reaction that produces biodiesel is the transesterification reaction. Esters of fatty acids are formed in the reaction between alcohol and triglycerides, which are the main constituents of fats and oils, in the presence of catalysts. In addition to edible, inedible and waste oils that can be used in biodiesel synthesis, the choice of alcohol is also quite wide. The synthesis of biodiesel from methanol and ethanol has been the most researched, but recently certain higher alcohols have also attracted interest. The alcohol of choice in this work is isopentanol which reacts with sunflower oil in the presence of a basic catalyst, potassium hydroxide. The influence of four reaction parameters on the yield of the transesterification reaction was monitored, namely: reaction time, molar ratio of alcohol and oil, mass fraction of catalyst and reaction temperature. The reaction time ranged from 0.5 to 2.5 h, the molar ratio of alcohol and oil from 4: 1 to 10: 1, the mass fraction of catalyst from 1 to 3 % and the reaction temperature from 40 to 80 ˚C. With the help of the Design Expert 11 software package, a Box-Behnken plan, containing 29 experiments, was created. Although it is most often used as a qualitative method, 1H NMR spectroscopy was used for quantitative analysis, i.e. to determine the yield of the reaction. Numerous graphical representations were analyzed which confirm or deny the coincidence of the experimental data with the model obtained with the help of the Design Expert 11 software package. In addition to determining the influence of reaction parameters on the reaction yield, the aim of this work was to find optimal conditions for the synthesis of isopentyl fatty acid esters. The software package offers the option of optimization and, depending on the wishes, the maximum and minimum importance of a certain reaction parameter is set, and as a result the synthesis conditions and predicted yield are obtained, which according to HRN ISO 14214 should be at least 95 %. By optimizing the process, it was shown that the maximum possible yield with a minimum amount of other reaction parameters is 98.56 %. If the desired yield is to be achieved, the transesterification reaction must be carried out for 2.43 h at a temperature of 78.64 ˚C with an alcohol to oil ratio of 8.86: 1 and a catalyst mass fraction of 2.57 %.