The search for producers of biologically active substances that overcome antibiotic-resistance is being actively pursued not only among extremophilic fungi, but also among inhabitants of unique ecological niches with special habitat conditions. These include the intestines of invertebrates: earthworms, millipedes, ants, termites, etc. Fungal spores are found in the stomachs and intestinal tracts of invertebrates. Interaction between fungi and invertebrates contributes to emergence of new compounds that are valuable for further development of antibiotic substances. In this work, we studied fungi associated with larva of black soldier fly Hermetia illucens grown on compound feed for laying hens. Inoculation of the contents of the intestine in the form of a suspension on agar nutrient led to the isolation of a fungal strain with pronounced antimicrobial properties. Phylogenetic analysis based on 18S rRNA revealed that the isolated strain belongs to the genus Byssochlamys. Culture liquid was extracted trice with ethyl acetate; residual antimicrobial activity was controlled by disc-diffusion assay. The culture liquid extract had a broad-spectrum of antimicrobial activity against a number of microorganisms: a fungus (Aspergillus niger INA 00760), a yeast (Candida albicans CBS 8836), gram-positive bacteria (Bacillus subtilis ATCC 6633, Staphylococcus aureus 29213) and gram-negative bacteria (Escherichia coli ATCC 25922). The culture liquid extract was fractionated by flash chromatography and HPLC; the antibiotic was isolated this way. Structure determination of the antibiotic is hampered by its ability to polymerize. Antimicrobial activity of the extract and fractions was monitored with agar well diffusion method and disc-diffusion assay. MIC of the pure substance was measured by the serial dilution method.