Abstract. 14 species of myrcomycetes of the class Leotiomycetes have been identified on decorative trees in the southern part of Uzbekistan. Species of the genera Uncinula, Phyllactinia, Leveillula, Microsphaera, Erysiphe are obligate parasites, and Marssonina, Melasmia, Rhytisma are considered facultative parasites and causative agents of dangerous diseases in trees. The species Rhytisma ulmi Fr., Melasmia populinae Rehm were first identified in the mycobiota of Uzbekistan. During a scientific study, 10 species of ornamental trees were found to be infecting representatives of the Leotiomycetes class. Including Salix dahynoides Vill. - 3, Ulmus pumila L. – 2, Populus alba are found in pairs, and in the species Acer negundo L., Sophora japonica L., Fraxinus sogdiana Bunge., Catalpa bignonioides Walt., Salix alba L., Quercus robur L., Robinia pseudoacacia L. one at a time.