Abstract: A significantsize effect is observed in tensile strength of solid particles such as ice, rock, ceramics and concrete. The tensile strength is not independent of the fragment size, but decreases with increasing size. Recent developments in fractal theory suggest that fractals may provide a more realistic representation of solid particles. In this paper, a fractal model for crushing of rock particle is constructed using the Steacy and Sammis model. The size effect of crushing strength is then derived. The size effect of the crushing strength is expressed by fdD-3. It is shown by the published data that the fractal dimension of the rock particle distribution is nearly 2.5-2.6. The size effect of crushing strength can be expressed by the fractal model for particle crushing.