The influence of oil-in-water nanoemulsion using commercial olive oil at different concentrations on the fatty acid profile of rainbow trout fillets stored at 4 +/- 2 degrees C was evaluated. At the end of the storage period, the highest content of the total saturated fatty acids (SFA) was found in the control samples (18.1%) while the lowest content was observed in olive oil samples (17.27, 17.59 and 17.48%). The concentration of total polyunsaturated fatty acid (PUFA) and monounsaturated fatty acid (MUFA) contents of treated samples remained relatively constant during the storage time while a marked decrease was observed in the control samples since olive oil-based nanoemulsion prevented the lipid oxidation. In addition, PUFA/SFA and n-6/n-3 ratios were found in good range, which are considered to be an important dietetic parameter. Olive oil used in oil-in-water nanoemulsion maintained the MUFA and PUFA contents of fish during storage and can be recommended as a preservative for fish.