We　present　the　electronic　structure　and　electron　energy　loss　spectroscopy　(EELS)　for　uranium,　niobium　and　U3Nb　in　which　uranium　is　substituted　by　niobium.　Comparing　the　electronic　structures　and　optical　properties　for　uranium,　niobium　and　U3Nb;　we　found　that　when　niobium　atom　replaces　uranium　atom　in　the　center　lattice,　density　of　state　(DOS)　of　U3Nb　shifts　downward　to　low　energy.　Niobium　affects　DOS　for　f　and　d　electrons　more　than　that　for　p　and　s　electrons.　U3Nb　is　similar　to　uranium　for　the　electronic　energy　loss　spectra.