The present paper provides a root biomass evaluation of seven European beech and seven Silver fir sample trees. The investigation was held in beech Ecological Experimental Station located in south-eastern part of Kremnickevrchy (The Kremnica Hills) near Zvolen, Slovakia. All data were obtained by a destructive sampling method. Below-ground biomass was determined from the first three tree-classes (according to Kraft). Below-ground biomass was analysed in weight when fresh and when dry according to diameter classes. The total root biomass of European beech reaches 47.68 t.ha(-1) in term of dry weight. The roots with diameter over 10 cm represent about one third of the whole below-ground biomass. The total below-ground biomass of Silver fir (30 % of species composition) is 15.13 t.ha(-1) The roots with diameter over 10 cm represent 40 % of total underground biomass. The most substantial root biomass was obtained in the second tree-class (trees from main canopy level).