Hair is a more biologically stable material than other tissues and contains a relatively constant level of minerals, drugs or toxins. The content of essential elements in hair depends on dietary and non-dietary factors. The aim of this study was to assess and compare the effect of diet on the elemental composition and morphological properties of the hair of healthy Polish Konik horses. Mane hair was collected from 19 horses living in The National Park in Popielno in Poland. Six of these horses were free-ranged all year with permanent access to pasture, while 13 horses were kept in the stable and fed oats, hay and straw. The samples were analyzed using a Scanning Electron Microscope combined with Energy-dispersive X-ray spectroscopy (SEM-EDS). Each hair was analyzed for its microscopic appearance and elemental Mg, Si, S, Ca, Mn, Co, Zn and Se content. No significant changes in the morphological properties and elemental composition were observed. There was inter- individual variability in element content between horses in both groups, but this did not affect their health. The comparison of the present results with other studies shows that the level of elements in the hair of Polish Konik horses is significantly lower than in healthy horses of other breeds. The traditional feeding plan containing pasture, oats and hay does not contain a sufficient amount of main mineral elements. Further investigation is needed to explain the effect of diet and maintenance on the mineral balance of horses.