The barium yttrium fluoride, BaYF5, can be simultaneously doped with divalent europium and some trivalent rare earth ions. The purpose of this paper is to enhance the understanding of some fluorescence properties of this optical materials which are rare earth-activated BaYF5 fluorides with potential pactical applications. The emission and excitation spectra, fluorescence lifetime of the Eu2+ and Ho3+ ions, and supersensitivity of Ho3+ absorption band (5I8→5G6) in the system BaYF5 have been investigated under excitation of nitrogen laser pulse. The emission Corresponding to the 5S2→5I8 transition dominates the Ho3+ spectrum. Energy tramsfer from Eu2+ to Ho3+ ion occurs. The experimental and theoretical results fit the Inokuti and Hirayama's equation. The mechanism of radia-tionless energy transfer is found to be dipole-dipole interaction. The critical transfer distance R0 is approximately 6?. Probabities and efficiencies of energy transfer have also been calculated.