The increase in the cohesive properties of fly ash under elevated temperature conditions up to 1123 K, was investigated by a diametral compression test of ash powder pellets. Under conditions of relatively low temperatures (below 1000 K), the strength of ash powder pellets increases gradually in proportion to temperature. A remarkable increase in strength of the powder pellets is observed in the high temperature range above 1123 K. At these high temperatures, plastic deformation (during a diametal compression test) and enhancement in the time dependent on increase in fracture load of ash powder pellets is observed.