Abstract: Due to the existence of various micro-defects in brittle or quasi-brittle materials, the mechanical behavior, such as the nominal failure stress, stiffness and fracture toughness etc., varies with the dimension of specimens. This is defined as the size effect of such materials. In general, the Bazant size effect law is established experimentally using a series of similar specimens. In this paper, a new experimental procedure by which the fracture toughness and effective fracture process zone length are measured using the specimens with fixed crack length is proposed, and the associated formulas are also presented. Under the condition that identical brittleness numbers must be ensured for both the proposed and commonly-used similar specimen method, relatively small specimens can be used under laboratory conditions. It is shown that and good agreement is reached in comparison with the results of the commonly-used similar specimen method.