Plant sterols (PS) are very stable molecules but may undergo oxidation due to the presence of a double bond in the ring structure. In order to assess whether this occurs during heating and storage, an analytical procedure was developed for the determination of concentration levels and identity of PS oxidation products in functional food ingredients and products. The method is based on cold saponification, solvent extraction of unsaponifiables, isolation of sterol oxidation products by means of liquid chromatography, and final analysis by gas chromatography (GC) with flame ionization detection. Identification of the key PS oxidation products was performed by means of GC-mass spectrometry (GC-MS). Isotope dilution MS was used to verify the absence of the formation of potential artifacts by the method. The method described is applicable to spreads (containing 20-65% water), oils, sterol esters, pure sterols, and fat extracts from food. The between-day reproducibility of the total content of sterol oxidation products in control samples sample was 8%, and of individual sterol oxidation products, 6-15%. The recovery of sterol oxidation products was 91%. The limit of detection was 0.1 mg/kg.