Three Kuiper Belt objects (KBO) of 23-24 V-magnitudes were observed with BTA-6m Telescope of the Special Astrophysical Observatory, Russia. CCD-photometry in BVRI bands was performed and the spectral curves of the KBOs normalized reflectivity were obtained and compared both with the ones published by Jewitt and Luu, and with the ones referred to Main Belt asteroids and comets nuclei. By occasion, an unknown Main Belt asteroid passed within 20" next to one of the KBOs in the same frame, which made it possible to compare the colors of the two bodies directly. Some hypotheses about chemical composition of KBO surfaces are proposed.