The aim of the study presented here was to find out the effects of storage at -30 degrees C on fatty acids in fish oil, without adding antioxidants. Oils of sardines from the Sea of Marmara were extracted, analysed and stored at +4 degrees C for 4 and 8 days, and thereafter at -30 degrees C for 24 months. Fatty acid composition analyses were performed initially and after 4 and 8 days as well as after 24 months. In the case of the fatty acids C-16:0, C-20:1, C-18:3, C-22:6, C-14:0, C-16:1, and C-20:5 considerable changes with regard to their concentrations could be observed. In general, there was a decrease in minor unsaturated fatty acid (MUFA) content, and an increases in the saturated fatty acid and in some polyunsaturated fatty acid (PUFA) content.