Abstract: To screen endophytic fungal resources with antagonistic effects against leaf spot disease of Malus sieversii, healthy leaves of Malus sieversii were collected from the Gongliu Wild Fruit Forest in Yili, Xinjiang. Culturable endophytic fungi were isolated using the tissue isolation method, and identified by combining morphological characteristics and ITS sequence analysis. The inhibitory effects of endophytic fungi against Alternaria alternata, the pathogen causing leaf spot disease, were determined by the plate confrontation assay. The results showed that a total of 25 ¹endophytic fungal strains were isolated and purified, which were identified as 10 genera, 8 families, 7 orders, 4 classes and 2 phyla. Among them, Ascomycota was the absolutely dominant phylum, accounting for 84.6%. The plate confrontation test indicated that 9 endophytic fungal strains exhibited an inhibition rate higher than 50% against A. alternata, with significant differences in the inhibitory effects. Strain E01 of Xylaria showed the strongest antifungal activity, with an inhibition rate of 64.35%. The antagonistic endophytic fungi obtained in this study, such as Xylaria , provide strain resources for the green biological control of Alternaria alternata in Malus sieversii.