The paper presents the results of studies conducted over 1995-99 which involved spring rape (Star and Lisonne cultivars) and over 1998-00 which - white mustard (Nakielska and Borowska cultivars) grown on experimental plots at Balcyny, of University of Warmia and Mazuria in Olsztyn (Poland). The aim was to evaluate the effect of selected herbicides on phosphorus, potassium and magnesium content in spring rape seeds and phosphorus, potassium, magnesium, calcium and sodium content in white mustard seeds. The herbicides applied neither demonstrated a significant effect on the content of the minerals investigated in spring rape seeds nor modified the content of most minerals in mustard seeds, except for sodium and magnesium in the first experiment year and phosphorus in the second year. Throughout the experiment cycle the spring rape cultivars tested differed significantly in the content of magnesium, while white mustard cultivars - only in the content of phosphorus