Forest gaps, openings in the canopy caused by death of one or more trees, are the dominant form of natural disturbance in the temperate forests. Gaps play a critical role in driving stand dynamics and influencing forest growth cycle. They increase habitat diversity, structural complexity, fauna and flora species diversity. The size of a gap may strongly influence tree species regeneration composition, vegetation growth, nutrient cycling, microclimate and may have considerable effect on a number of biological processes. The main aim of this study was to understand the effects of gap size diversity on species composition and number of natural regeneration. The study was carried out in near−natural mixed stands dominated by beech (Fagus sylvatica L.) and silver fir (Abies alba Mill.) representing different development stages and phases in the Świętokrzyski National Park, (central Poland). All gaps over than 20 m 2 intersected by a transects line were sampled. All saplings and seedlings were counted in circular plots (10 m²) evenly spaced along the long axis in the N−S and E−W gradients of each gap. Natural regeneration was analyzed for 62 canopy gaps of various sizes. The gaps were classified into three size classes: small ≤100 m², medium 101−250 m² and large >250 m². The gap size ranged from 21 to 397 m², with a median of 104 m². The dominant tree species regenerated in gaps were fir (69%) and beech (24%). The number of regeneration significantly depended on the gap size (p=0.027). The highest frequency of saplings was found in gaps of ≤100 m². The number of natural regeneration was significantly negatively correlated with gap size (r=–0.261, p=0.040). The density of silver fir regeneration was significantly higher in gaps of ≤100 m² and 101−250 m² (p<0.05). The share of fir in stand species composition effected on the number of silver fir and European beech regeneration. The results of this study demonstrated the utility of gap−based approach for better understanding ecosystem responses to tree cutting for modern forest management.