The present study aimed to examine the impacts of small (85.12 m2), medium (325.21 m2),large (512.11 m2) and very large (723.85 m2) gaps on soil properties in a mixed beech – hornbeamstand of northern Iran. As well as the value of pH, organic matter and carbon, total nitrogen, cationexchange capacity (CEC), phosphorus, potassium, calcium, nitrogen mineralization, microbialrespiration, earthworms density and biomass of soil samples (0 – 15, 15 – 30 and 30 - 45 cm depthsfrom gap center, edge and closed canopy positions) were measured in laboratory. Significantlyeffects of gaps size were found on soil properties as the highest values of CEC, density and biomassof earthworms observed in small gaps. The highest values of carbon to nitrogen ratio, phosphorus,potassium and calcium were detected in medium gaps. The most amounts of organic matter andcarbon, nitrogen mineralization devoted in very big gaps. Greater amounts of pH, total nitrogenand microbial respiration were detected in big and very big gaps. It was found that gap positionhad a profound effect on soil characters as the highest values of pH, organic matter and carbon,total nitrogen, phosphorus, potassium, calcium, nitrogen mineralization, microbial respirationobserved in gap center. The greatest amounts of carbon to nitrogen ratio, CEC, density and biomassof earthworms were detected in closed canopy. According to the results, soil upper layers showedthe highest values organic matter and carbon, soil nutrition elements and biochemical activities,whereas the highest amounts pH, carbon to nitrogen ratio, CEC and density and biomass ofearthworms were observed in deeper soil. It is concluded that opening areas of canopy covershould be less than 400 m2 in beech forests of northern Iran with considering of soil properties.