The aim of this study was to assess the composition of fatty acids, including unsaturated fatty acids in trans configuration, in different types of milk desserts purchased at the local market in Olsztyn. Determinations were performed with the GC method, with the application of an HP 6890 gas chromatograph equipped with a flame ionization detector (FID) and a 100 m long capillary column with CP Sil 88 phase. The desserts analysed were characterised by different contents of fat, ranging from 2.0 to 12.9%. Contents of particular groups of fatty acids were as follows: higher saturated fatty acids – from 58.76 to 69.77%, monounsaturated fatty acids – from 18.03 to 28.83%, polyunsaturated fatty acids – from 2.25 to 3.98%, and volatile fatty acids – from 6.57 to 10.18% of total fatty acids in the desserts fat. Fat isolated from all analysed desserts was confirmed to contain trans isomers of C18:1 acid, cis, trans and trans,cis isomers of C18:2 acid as well as cis-9, trans-11 isomers of CLA.