A　new　Li2O-SrO-Nb2O5-P2O　5　glass　system　was　prepared　by　a　high-temperature　alumina　crucible,　and　structural　characterization　and　optical　properties　were　investigated.　Proper　content　of　Li2O　and　Nb2O5　was　employed　to　replace　partial　SrO　and　P2O5　to　improve　the　optical　properties.　It　was　observed　that　the　enhancement　of　the　refractive　index　from　1.75　to　1.85　is　mainly　due　to　the　Nb2O5　content.　An　addition　of　Li2O　significantly　increases　the　optical　transmittance;　optical　transparency　can　be　enhanced　from　60%　to　higher　than　85%　in　the　UV-visible　region　with　addition　of　20-40　mol%　Li2O　species.　However,　optical　transmittance　is　monotonically　decreased　from　about　90%　to　80%　under　10-30　mol%　Nb2O5　addition.　The　40P2O　5-20Nb2O5-20SrO-20Li2O　glasses　demonstrate　the　optimum　refractive　index　(n　＞　1.75)　and　high　optical　transparency　(＞80%)　in　the　UV-visible　region.　Furthermore,　the　effect　of　Nb2O5　on　the　structural　transition　was　focused　on　the　(60　-　y)P2O5-yNb2O5-20SrO-20Li　2O　vitreous　system　since　the　transition　of　FTIR　spectra　reveals　that　the　Nb2O5　has　more　pronounced　effect　than　Li2O　in　the　glass　network　due　to　the　higher　covalent　extent　and　electronegativity.　Addition　of　Nb2O5　generates　Nb-O　bonds　by　dissociating　P-O　chains　and　results　in　the　decrease　in　the　intensity　of　the　(PO2),　(POP),　and　(PO3)　absorption　bands.　The　O1s-XPS　analysis　shows　that　Nb2O5　addition　dissociates　symmetric　bridging　oxygens　in　P-O-P　bonding　and　forms　asymmetric　bridging　oxygens　in　P-O-Nb　and　non-bridging　Nb-O-　bonds,　in　which　octahedral　[NbO6]　unit　is　eventually　substituted　by　[NbO4]　tetrahedral　unit　in　the　Li-Sr-Nb　phosphate　glasses.　©　2014　Elsevier　B.V.　All　rights　reserved.