Establishment of natural regeneration inside gap canopy is one of the challenges for forest managers so collecting of information about how the gap canopy could effects on quantitative and qualitative characteristic of seed germination of trees especially pioneer species is so valuable. To achieve this goal, 24 canopy gaps were identified from a mixed Fagetum stand at Hajikola-Tirankli forestry plan from Tajan River watershed. In the following, the canopy gaps were classified to three difference size classes such as smaller than 150 (small), 150-350 (moderate) and 350-500 m² (large) and the seeds of the Acer velutinum and Diospyrus lotus as pioneer species were collected from inside and outside of the canopy gaps and seed germination test were done on the collected seed. Seed germinant percent and germination speed were calculated and then statistically analyzed. The results about Acer velutinum showed that although seed germination percent of the species wasn’t different between inside and outside of the canopy gaps, seed germination speed of the pioneer species was higher in collected seeds from inside than those collected from outside of the canopy gaps. Seed germination percent of Diospyrus lotus collecting from inside of canopy gaps with 150-350 and 350-500 m² sizes were higher around 20% than those collected from next control stands. Moreover, the highest seed germination speed was observed in collected seeds from large canopy gaps. Overall, the positive effects of canopy gaps with 150-500 m² area in keeping seed germination conditions of the both species was proven by the current research.