Abstract: In this paper, the effects of material property and specimen’s size on the mixed mode fracture behaviors are studied by theoretical analyses and tests. Results show that mixed mode fracture behaviors are related with material property. I-II mixed mode crack growth paths are almost independent on the material property and consistent with the brittle fracture criteria. It is considered that the brittle fracture mechanism play a dominant role for materials within δ%≤13, when CTS specimens are under I-II mixed mode loadings. While I-III mixed mode crack growth paths are almost independent on the material property. There exists an obvious ductile-brittle transition as δ% decreases for materials within δ%≤13, when CTS specimens are under I-III mixed mode loadings. Conclusions in this paper provide a reference on the mixed mode fracture evaluation, and promote the progress of fracture mechanics.