Ultraviolet photoluminescence (PL) of LiB3O5 (LBO) crystals has been studied under selective excitation by photons in the vacuum ultraviolet and ultrasoft x-ray regions, including the K-absorption edges of the Li and B cations and O anion. Radiative recombination of electron-hole pairs was established to be the main channel of the intrinsic PL excitation at 4.2 eV. Features were observed in the PL excitation spectra near the lithium and boron K-absorption edges originating from excitation of the cation 1s core excitons. Experimental evidence of the multiplication of Li 1s excitons in LBO was obtained. It is shown that excitation of the O 1s core excitons does not affect the PL yield noticeably. The differences in the appearance of the Li, B, and O 1s excitons in the excitation spectra of the LBO ultraviolet PL are discussed.