The objective of the analysis was to assess butter sold at the Polish market from the point of view of its composition that could potentially be adulterated by replacing milk fat with plant oils. Liquid chromatography (HPLC) was applied to qualitatively and quantitatively determine two organic compounds, appearing characteristic for plant oils: Tocopherol (-T) and tocotrienol (-T3) in the samples of butter. At the retail market, slabs of butter were randomly bought called Extra, Śmietankowe, and Osełkowe; those slabs of butter were analysed. It was found that 33% of all the butter samples analysed were manufactured with plant fat added because they contained tocopherols, and, in particular, tocotrienols, which occurred exclusively in palm or in coconut oils. The percent rate of these homologues in the total content of tocochromanols ranged from 40 to 82%. The quantity of tocochromanols identified proved that various amounts of plant oil have been added to milk fat; it also meant that there were unreliable manufacturers on the Polish market who showed solely the content of milk fat (82 or 73.5%) on the packages of their butter.