The aim of this work was to examine the fatty acids composition, especially trans isomers (TFA), and oxidative stability of frying fats available on the Polish market. The quality of 23 frying shortenings of Polish origin or imported, produced in the years 1997 and 2008, was estimated in the study. Their fatty acid composition was determined with the GC. The fats examined differed substantially in the content of TFA. Only about 33% of fats from 1997 and about 46% from 2008 contained very small contents of these acids (below 1%). Some of fats were characterised by a high concentration of TFA (about 50%), thus we could assume that these fats were based on raw materials modified by partial hydrogenation. A reduction of TFA content of the frying fats was noted from 1997 to 2008. It was found that an average TFA content in frying fats sold in Poland in 1997 was 21.4%, while in 2008 it was significantly lower and reached 12.2%. TFA had a positive, but PUFA a negative influence on induction period of fats.