The early hydration of ordinary Portland cement (OPC) pulverized fly ash (PFA) blends with various PFA proportions was investigated using microwave technique and conduction calorimeter. It is found that PFA acts as almost inert filler in the OPC/PFA blends during the first 40 h of hydration, thus it retards the early hydration of the blends. To accelerate the ponolanic hydration of the PFA, three different additives were studied. It is found that both Ca(OH)(2) a nd Na2SO4 can accelerate the early hydration of the OPC/PFA blends, but Na2SO4 is more effective than Ca(OH)(2), whereas NaOH is not suitable for the acceleration of the early hydration of the OPC/PFA blend.