The Hertzian indentation technique has been evaluated as a possible means of assessing the surface fracture behaviour of a set of qualitatively similar liquid phase sintered polycrystalline aluminas with systematically varied composition, and a range of grain sizes. The method provides a better correlation between microstructure characteristics and surface fracture behaviour than does Vickers indentation. The fracture toughness determined from Hertzian indentations was found to be a function of grain size, irrespective of the composition of the material. The cumulative probabilities of formation of ring cracks at specific loads during indentation with a spherical indenter were determined for each material from the set of 25 measurements, and the parameters of distribution of the probability of fracture were calculated. A statistical correlation between the failure probability distribution and the size distribution of alumina grains was detected.