The fast ionic conductor, LiCl-LiF-B2O3, LiF-B2O3 in microcrystalline and non-crystalline forms were studied by positron annihilation. It was found in all cases, the intensity of the mid-lifetime component I2 depends directly on the electrical conductivity σ. Additional measurement of Doppler broadening on the same systems indicated that voids between the microcrystal and network phases provid more transfer path for Li ions, thus lead to higher conductivity in the microcrystalline form of LiCl-LiF-B2O3 system.