The transparent glasses 55 P₂O ₅ - (45-x) Na₂O - xLi₂O where (x=0, 3, 10, 15, 30, 35) were prepared by conventional melt quenching technique. Structural and characterization have been investigated by using X-Ray diffraction (XRD) and the results show that all samples are amorphous structure. The glass transition (T_g) and crystallization temperature (T_c) are evaluated using the differential thermal  analyzer (DTA), which indicate that 15 mol% Li₂O contained glasses exhibits maximum thermal stability h' of  glass samples. Density, molar volume and oxygen packing density insure that Li₂O incorporated in sodium phosphate glass by increasing Li₂O content. The ac and dc electrical conductivity and dielectric constants of the prepared glass samples have been investigated. The variation of dc conductivity with the concentration of Li₂O mol% passes through a maximum at 15 mol% Li₂O. Temperature dependence of the dc conductivity of these glasses is found to obey the Arrhenius law. It reveals that the values of activation energies ΔE_dc1 and ΔE_dc2 at low and high temperatures lie in the range 0.452-0.93 eV. Also it was found that the values of σ_dc to be the same as the values obtained from the impedance study. Conductivity mechanism for grain resistance at room temperature was discussed using Cole-Cole plot. To determine the conduction mechanism, the ac conductivity and its frequency exponent have been analyzed by correlated barrier hoping model (CBH). It was found that the exponent (s) has values between 0.62-0.9; consequently the (CBH) seems to be the most interesting model related to the obtained results. The variation of dielectric constants ε' and ε'' with the concentration of Li₂O mol% pass through a maximum at 15 mol% Li₂O and this result would be discussed by means of dielectric polarization mechanism of material. The maximum value of the maximum barrier height W_m obtained from Guitini equation was found to increase with increasing of Li₂O mol%.