The taxonomic structure of microscopic fungi complex in root zone of sunflower under its growing in conditions of southern Steppe of Ukraine comparing with natural biocenosis and black vapor has been studied. Soil of background (natural biocenosis rhizosphere) black vapor (arable layer 0'20 cm) and root zone (rhizosphere) of a sunflower hybrid Zaporozhsky-32 was investigated. Soil samples of sunflower rhizosphere were selected at the stages of 2'4 true leaves (May) flowering (June) head formation (August) and full maturity (October) during 2009'2011. Samples of background soil and black vapor soil were taken in the same terms as the crop. Almost throughout the entire vegetation period the number of micromycetes in the root zone of sunflower did not differ from the natural biocenosis and black vapor and only by the end of the vegetation it nearly doubled. Despite almost the same total number of identified genera there are significant differences in genus composition of micromycetes isolated from background soil and root zone of sunflower. Micromycetes of the genera Botrytis Cladosporium Metarrhizium and Rhizopus were typical only for sunflower rhizosphere while micromycetes of the genera Doratomyces and Acremonium were exclusively found in natural biocenosis. In addition in soil under sunflower the range of the species in Penicillium genus expanded while the species variety in Aspergillus genus significantly reduced compared to background soil and black vapor. During the growing season in natural biocenosis genus diversity practically did not change whereas in root zone of sunflower some fluctuations in number of genera were observed. Based on the Sorensen index it was found that the micromycete complexes of the background soil and the black vapor were the most similar where 23 species of fungi were common while in rhizosphere of sunflower very specific mycocenosis was formed.