Nanoemulsions have recently attracted increasing attention, compared to conventional emulsions, due to their specific properties. Small droplet size, high kinetic stability, and tunable optical transparency (milky-white to transparent) are making them suitable for wide range of applications, especially in pharmaceutical industry, with the possible use as improved drug carriers. The focus of this diploma thesis was formation of O/W type nanoemulsions, with soybean oil as a dispersed phase. Four different surfactants were used (in ascending concentrations): Polisorbate 80, Polisorbate 60, Pluronic F68, Cremophor EL. The nanoemulsions were formed using microfluidisation as a high energy method of preparation. The main measured parameters were droplet size, polydispersity index and zeta-potential. Each of them was determinated two times. The first measurement followed the preparation by microfluidisation. The second one took place 10 days after the preparation process. The purpose of the second quantification was to determine the effect of time on nanoemulsion stability. The results of the droplet size measurement show the decrease of the droplet size in correlation with the increase of surfactant concentration in the formulation. The value of PDI, on the other hand, rises. All of the samples with the surfactant concentration of 2,5% (m/m) or above, showed the unsuitable PDI values, which indicates their instability towards the Ostwald rippening and flocculation process. Measurement of zeta-potential shows the low negative surface charge of the droplets, which can be a result of free fatty acids that come from the soybean oil. The values measured 10 days after the microfluidisation do not differ greatly from the measurements made directly after the preparation, except for the zeta-potential values of samples with Polisorbat 60, where the significant increase can be seen. Taking all results into account, it can be concluded that the nanoemulsions with Cremophor EL are the most suitable for further use.