A study on nonisothermal crystallization kinetics in fly ash (FA) filled isotactic-polypropylene (PP) composites has revealed some interesting phenomena. Composites made by injection moulding of PP with 0, 20, 45, and 60 wt of FA were nonisothermally studied using differential scanning calorimetry at cooling rates 10?C, 15?C, and 20?C per min from a melt temperature of 200?C cooled to -30 ?C. Whilst neat PP showed a mono modal a crystalline phase- only structure, presence of FA led to bimodal thermographs revealing partial transcrystallisation of a into b, to maximum 14 . The onset and peak crystallization temperatures of all samples decreased by 3?C with each 5?C/min increase in cooling rate. Parameters such as crystal growth rate, dimensions, and activation energy were determined using a series of established models. The Avrami graphs showed that contrary to the published data, there are two sets of straight lines (a) with a lower slope at low cooling rate and (b) with a distinctly higher slope for high cooling rate. Activation energy of the materials reached a maximum at 45 FA.