The Weibull strength distributions and fracture characteristics of three abrasive grains, brown corundum, white corundum and green silicon carbide, are investigated. The effects of the surface defects from crushing and the inherent microcracks from processing prior to crushing on fracture strengths and characteristics of the abrasive grains are discussed together with SEM observations. A novel proof-testing has been carried out in terms of low energy ball milling so that survived abrasive grains have improved strength characteristics. Strength distributions before and after the proof-testing have been compared. It is concluded that the strength of larger grains is strongly influenced by surface defects due to crushing, and the strength of smaller grains is more relevant to the inherent processing microcracks and pores formed during the manufacturing process prior to crushing. The influence of processing conditions, such as fusing and sintering, on strength distributions of the brown corundum is also discussed.