Abstract In general, it is well known that the energy efficiency of a grinding process decreases with decrease in produced particle size, increase in grinding time, or increase in input energy. In this paper, a grinding method, based on fracture mechanics, to produce ultrafine particles has been investigated. We define the size reduction energy as the elastic strain energy which is stored in the specimen up to the instant of fracture. Assuming that the kinetic energy of a grinding medium or a particle were converted completely into fracture energy, the relationship between impact velocity required to fracture and particle size, or between impact velocity of a grinding medium required for a particle to fracture and mass of a medium have been calculated. As a result, the assumption that, for ultrafine grinding, a grinding medium collides against a particle was found to be more feasible than that a particle collides against a medium. It was necessary to increase the collision probability because the number of particles produced varies inversely as the cube of particle size. The experimental verification of the above considerations was performed using a ball mill. Ground products smaller than 3 μm with a median diameter of about 0.3 μm were obtained.