Fragmentation experiments of quartzite particleswere carried out in a laboratory-scale hot fluidized bed. The influences of the factors, the initial particle size (2.5–6mm) and the bed temperature (650–950 ◦C),on the fragmentation were investigated. The experimental results indicate that both the fragmentation ratio (Nf) and the fragmentation index (Sf) curves show a nearly linearly increase with the initial particle size from 2.5 to 6mm or with the bed temperature from 650 to 950 ◦C. The changing ratio of size (Fd) is relatively invariant with the initial particle size at all considered bed temperatures except the initial particle size of 5–6mmat which Fd shows amore intense reduction at a higher bed temperature as a whole. The extent of the fragmentation is quite limited when the bed temperature is lower than 750 ◦C and the initial particle size is smaller than 3mm. The analysis of the quartzite particles size distribution after fragmentation shows that it is the compressive and thermally induced stresses within the outer region of the particle that causes the particle to fracture with many small fragments on the particle surface. Finally, based on the grey theory, a grey forecasting model GM(1, 3) is developed to predict the thermal fragmentation of the quartzite particles. The comparison demonstrates that the forecasted values are in good agreement with the experimental data, and the average residual error is lower than 7.13%. Using the model GM(1, 3), the critical fragmentation diameter (dc) under different bed temperatures is forecasted.