The xLi(2)O-(1-x)(yB(2)O(3)-(1-y)P2O5) glasses system is one of the parent compositions for chemically and electrochemically stable solid state electrolyte applicable to thin film battery. The purpose of this study was to seek an optimum composition maximizing the ionic conductivity for the deposition of thin film electrolytes. xLi(2)O-(1-x)(yB(2)O(3)-(1-y)P2O5) glasses were prepared with wide range of composition, i.e. x=0.40-0.47 and B2O3/B2O3 + P2O5) ratio was 0. 17-0.67 (y = xx similar to xx). The structural variation of the oxide Li2O-B2O3-P2O5 system was investigated by Raman spectroscopy to find out the correlation with the electrical conductivity. It was shown that under 40 mol% of Li2O the ionic conductivity monotonically increasedwith increasing of B2O3, while overthe 40 mol% of Li2O it exhibited a maximum at a specific B2O3/(B2O3+P2O5) ratio, typically similar to 0.5. The structural investigation indicated that the variation in conductivity was closely correlated to the variation of 4-coordinated boron groups. (c) 2007 Elsevier B.V. All rights reserved.