With plot cruising and rout investigation methods, 36 species of ectomycorrhizal fungi associated with oaks were found in natural secondary oak forest in Dandong district of Liaoning Province. They were subordinated to 7 familyies, 13 genera. Studies on the relationship of the ecological distribution of mycorrhizal fungi with tree species, tree age and seasons showed that 29 species mycorrhizal fugi preferred to grow with Q. mongolica, The species of Russulla were associated with a wider tree ages of oak, and the species of Amanita were most likely to grow with old tree. July and August were the occurrence peak of mycorrhizal fungi. 75% species occurred in July, and 100% species occurred in August. The relative density of the occurrence number was the highest in mid-August (19.5%) and last-August (18.4%).