Abstract: Based on brittleness evaluating index of concrete, the normal concrete, fly ash concrete, lightweight aggregate concrete, fiber concrete and polymer-modified concrete were selected as sample, and the size effect on flexural strength by the method of the Bazan's size effect law was presented to show the brittleness degree of concrete.The Bazant's size effect law gave a very good fit to the flexural strength of concrete measured from beams of different sizes.As observed in the size effect curves, the fracture behavior of lightweight concrete seemed more brittle than that of the other HPC, and fiber concrete and polymer-modified concrete showed less brittle than normal concrete, moreover, fly ash was less benefit for brittle decreased.Linear elastic fracture mechanics may still be less applicable to concrete in the normal size range than nonlinear fracture mechanics.