The urgent need to produce different sealing glass with distinct thermal properties, recommended to study the behavior of phosphate glass system. Binary alkali phosphate glasses are characterized by low viscosity, low melting temperature, and proper thermal expansion. However, it has poor chemical durability. Therefore, work must be done to improve its chemical properties to suit practical applications. The effect of replacing different proportions of sodium oxide (Na2O) in equimolar sodium phosphate glass system by equivalent portion of divalent metal oxide on the thermal characteristics was investigated. Thermal expansion coefficients were determined experimentally and theoretically. Careful analysis of dilatometric curves of thermal expansion helps to define both the transition temperature Tg and the softening temperature Td. It can be found that, both of Tg, Td temperatures were increased with increasing divalent metal oxide content. This is a clear indication to improve the crosslinking and decrease of the non-bridging oxygen atoms. Also, this observation is consistent with the density results and IR data.