The effects of substrate materials on the design of microstrip power divider are investigated theoretically and experimentally. Three different dielectric substrate materials are chosen ; Duriod 3003, G10/FR4 epoxy Glass and Duriod 3010 to be studied. A three-way double-stage power divider is designed at S-band frequency of 2.25 GHz and etched on each studied substrate separately. The substrate effects of large difference in dielectric constant and the dissipation factor ; on the characteristics and performance of the microsrip circuits are taken into consideration in the present study. The circuit designs presented here, are analyzed using the Genesys CAD program and implemented and tested experimentally. The simulated and measured results are compared , discussed and indicate that significant changes in the characteristics of the microstrip power divider are observed.