The purpose of the thesis was to study gap dynamics and establish a permanent research plot (0,8 ha) in old-growth forest reserve Donačka gora. North- American approach (line intercept sampling) was used for canopy gap survey. The old-growth forest reserve Donačka gora encompasses 39,15 ha. We used only most preserved core area for our research which was done in 2011. On three transects we captured 39 gaps and 144 gap makers. Gap and expanded gap fractions reached 12,6 % and 41,9 %, respectively. The mean gap size was 231,57 m2, 57 % of the gaps were smaller than 200 m2. It was found out that gap makers in gaps are appearing in different phases of decay, which implies progressive spreading of gaps. Analysis showed that most of the gaps include 2to 5 gap makers. Small-scale regeneration patterns were observed within gaps,the main tree species in regeneration and in upper canopy layer was beech. Light demanding tree species were successfully regenerated only in gaps larger than 500 m2. Analysis of data from research plot showed that the density of live trees was 175 trees per hectare and volume of live trees reached 496 m3/ha. Frequency distribution of diameters of live trees on the plot was close to negative exponential, which indicates uneven structure of the forest. The volume of dead trees reached 158,20 m3/ha or 24,2 % of the total growing stock on the plot, which shows old-growth characteristics of these stands. Within the dead trees downed trees prevailed, their share reached 83,4 % of the total volume of dead trees.