The aim of this study was to determine the concentration of heavy metals (Cd, Pb, Hg and As) and essential elements (Fe and Se) in fallow deer tissues (muscle, kidney, liver, adipose tissue and spleen) before the addition of selenium in the food and after that to determine the interaction of selenium with heavy metals in the tissues and the influence of selenium on immunohaematological (CBC and WBC), biochemistry (glucose, urea, CRE, ALB, TGC, KOL, HLD, LDL, Fe, TP, GLOB, IgG) indicators and indicators of oxidative stress (SOD, GPx, GSH and vitamin E). The research was conducted on 40 fallow deer that were shot in the hunting season during the two year research. Analysis of habitat included analyses of soil, tree leaves, grasses and fodders. Supplemental nutrition with the addition of selenium (0.5 mg/kg) was carried out for 60 days in the second year of the research. During the first year of the experiment there were increased concentrations of Cd and Pb in the tissues of fallow deer whereas concentration of Se was low. After supplementary feeding with the addition of selenium, concentration of heavy metals in the tissues was lower and antioxidant protection was improved. Addition of selenium had no negative impact on other tested parameters.