The paper presents the possibility of producing polyhedral oligomeric silsesquioxanes (POSS) under hydrothermal conditions in a high-pressure reactor. POSS was prepared by hydrolytic polycondensation of cyclohexyl trichlorosilane under conditions of elevated temperature and pressure. Morphology and structure of the final products were characterized by X-ray diffraction (XRD), thermal analysis (TGA and DTA) in an atmosphere of argon, Fourier transform infrared spectrum (FT-IR) and scanning electron micrograph (SEM). The resulting compound is a nanofibers of a polyhedral oligomeric silsesquioxane. The diameter of the obtained nanofibers is 50 … 150 nm, and the length is from 200 nm to 30 μm.