Magnesium fertilization of soil has been recommended as one of the ways to limit unfavourable effect of heavy metals on plants. Its effect may be connected with diminished heavy metal uptake by plants and changes in macroelement content. Therefore, the same measure may also change the host plant usability for potential herbivorous insects. The paper contains compiled results of research on the effect of magnesium fertilization under conditions of soil contaminated with single heavy metals to level III of soil pollution according to the IUNG classification, on the foraging of Bruchus rufimanus Boh. and Sitona (Sitona sp.) on broad bean (Vicia faba L. ssp. maior). It has been found that the applied fertilization level of soil contaminated with heavy metals does not affect significantly the yield of broad bean seeds, the degree of their damage due to Bruchus rufimanus or their germinating ability. Magnesium fertilization may slightly increase germinating energy of broad bean seeds from plants growing on cadmium contaminated soil. The effect of magnesium treatment under conditions of soil contamination with heavy metals on harmfulness of Sitona beetles to broad bean may be modified by atmospheric conditions in individual seasons. Magnesium fertilization of soil polluted with copper, lead, nickel and zinc to level III of soil pollution according to the IUNG classification does not lead to an increase in the degree of broad bean leaf damage by Sitona beetles. On the other hand, magnesium fertilization of soil contaminated with cadmium to level III of soil pollution in the IUNG classification may enhance broad bean plants’ attractiveness to Sitona.