Despite the numerous investigations on the phenolic composition and antioxidant properties of different plant tissues, there are only a few studies about forest tree leaves, moreover, the monitoring of seasonal changes is an underexplored area. The present investigation aimed to provide a comparative analysis of the antioxidant properties of the leaves from 12 selected Hungarian coniferous and deciduous forest tree species, during the vegetation period. From the methanolic extracts, the total phenol, flavonoid and flavan-3-ol contents were determined, as well as the 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and ferric reducing ability of plasma (FRAP) antioxidant capacities. The investigated species revealed diverse seasonal tendencies in their chemical parameters, including seasonal extremities. According to results, polyphenols had a determinant role in the antioxidant efficiency of the leaf extracts. The evaluation of the overall antioxidant power was accomplished by a scoring system. The species with the highest antioxidant capacity values (scores) were: European hornbeam (Carpinus betulus L.)>sweet chestnut (Castanea sativa Mill.)>Turkey oak (Quercus cerris L.)>downy oak (Quercus pubescens Willd.)>pedunculate oak (Quercus robur L.). The leaves of the listed species could be future sources of food antioxidants and nutritional supplements.