Fly ash samples collected from the hoppers of various electric fields of electrostatic precipitator attached to two different units (1 and 2) of a Super Thermal Power Plant were critically examined in respect of their particle size distribution and shape. Particle size analysis of each of the samples collected over a period of three months from the dust hoppers of seven fields of each unit (unit I and 2) reveals that in general ash particles collected from the hoppers of field I are coarser and show bimodal distribution. Ashes from hoppers for other fields of electrostatic precipitator are finer Ashes from unit 2 have a smaller particle size than those of unit I. The particle size of the ashes decrease along field I to field 7 for both units, with field 7 ashes being the finest. Ashes from fields 5-7 of both the units contain significant amounts of ultra fine particles (particle diameter phi < 5 mu m). Shape analysis reveals that ash particles of fields I and 2 are irregular in shape and the rest are spherical. The spherical nature of ash particles increases in the sequence of fields 3-7. Ashes of fields 6 and 7 of each unit are suitable for use as fillers/partial replacement of cement in high performance concrete due to an enhanced "ball bearing effect."