Composites of isotactic semicrystalline polypropylene (PP) reinforced with fly ash (FA) particles (particle size 5-60 mu m) were prepared by injection moulding at 210 A degrees C incorporating 20, 45 and 60% by weight of fly ash. Tensile tests were carried out at 25, 50 and 70 A degrees C. WAXRD, DSC and SEM studies were also undertaken. Modulus of elasticity of all composites at all temperatures was higher than that of the corresponding PP samples-the gain ranged between 10 and 60%. The strength of the composites had a mixed trend. At 25 A degrees C, the composites suffered significant loss in strength, as much as 47%, whereas, at 50 and 70 A degrees C, there was up to 15% gain in strength. Strain to failure of the composite samples ranged from as low as 6% at 25 A degrees C to over 50% at 70 A degrees C, coinciding with increase of Pukanszky parameter from 1.5 to 4.1. WAXRD and DSC tests confirm that FA is nucleator of beta-crystalline phase the amount of which increases to a maximum of 11% with increasing FA. SEM studies indicated that the polymer had a distinctly high lamellar ductility and showed interfacial interaction with FA in 20% FA composites at 50 and 70 A degrees C. The -OH group on the surface of FA appears responsible for the formation of interfacial interaction with PP chain. Notched Charpy tests showed a maximum gain of 58% impact energy for the composite with 45% FA, tested at 70 A degrees C over that of pure PP at 25 A degrees C.