ABSTRACT The leaves of sea-buckthorn (Hippophae rhamnoides L.) can be a rich source of nutrients and biologically active substances. Their levels depend on growing conditions, agricultural technology and climate. The studies however, mainly focus on nutritious value of fruit and seeds and there is shortage of the information regarding to buckthorn leaves. The aim of the experiment was to determine the effect of symbiotic mycorrhizal fungi on the chemical composition and antioxidant activity of sea-buckthorn leaves. The study was conducted in 2014 and 2015 at the Experimental Station in Lipnik, Poland. Mycorrhization improved the nutritional value of leaves of sea-buckthorn by increasing levels of total protein (3%), N free extract (1%), Ca (9%), Na (16%), Fe (18%), Cr (34%), and partially elevating antioxidant activity by increasing the concentration of polyphenols (7%). Leaves of 'Habego' had a higher nutritional value, containing more total protein (4%), crude fat (7%), crude fiber (30%), and all fractions of dietary fiber. 'Hergo' had more beneficial levels of minerals (P-27%, K-67%, Mg-4%, Na-30%, Zn-8%, and Cr-21%), polyphenols (51%), total flavonoids (35%), carotenoids (10%), and L-ascorbic acid (8%), as well as higher antioxidant activity (40%). The results of our study partly confirmed the earlier scientific reports on the impact of mycorrhiza on the chemical composition of plants. However, it is not possible to compare our results with data on berry plants, including sea-buckthorn, due to the lack of information in the literature.