In order to prohibit the delay of early stage hydration activator Na2SO4 was added to Fly Ash blended ce-ment and its effects were investigated. Various measurements such as Compressive strength Heat of hy-dration Pore size distribution Hydration products Microstructure were evaluated and the results show that specimens of Fly Ash(50wt%) with 5% Na2SO4 dramatically improved the compressive strength because pozzolanic reaction of Fly Ash and the formation of ettringite make th microstructure denser than OPC and flyash cement paste.