The objective of this study was to compare density, vegetative cover, basal area, height growth, aboveground biomass production, frequency, floristic composition, and species diversity of understory vegetation growing in Hungarian oak (Quercus frainetto Ten.), Oriental beech (Fagus orientalis L.) and a mixed stand of both species (90% Hungarian oak and 10% Oriental beech) with the same crown closure. Understory vegetation was sampled with a quadrat of 0.5 m x 1 m along the 25 m-long transect lines in each stand. A total of seventeen perennial plant species from thirteen different families were found in the three stand types and all of them were present in Hungarian oak stand, eleven in Oriental beech stand, and seven in the mixed stand of Hungarian oak and Oriental beech trees. Results showed that stand types had a statistically significant effect on density vegetative cover, basal area, height growth, biomass production, frequency, floristic composition, and species diversity of understory vegetation. Total understory vegetation density was the highest for Hungarian oak stand with about 136 plants m(-2) and the lowest for the mixed stand of Hungarian oak and Oriental beech with 44 plants m(-2). In addition, the Hungarian oak stand had the most diverse understoty vegetation with about 4.3 different plant m(-2), followed by the Oriental beech stand with 3.7 plants m(-2), and the mixed stand of the Hungarian oak and Oriental beech with 2.7 plants m(-2), Species density and diversity were the highest in Hungarian oak stand whereas aboveground biomass production and height growth of understory vegetation were highest in the mixed stand.