Impact fracture experiments were performed using three CT type specimens made of PMMA with the size ratio 1:2:3 with analogous geometry. A precrack was introduced artificially in each specimen, which was subjected to impact by a wedge bar. The flyer was accelerated by a gas gun to impose an impact force to the wedge bar, and the fracture behavior was measured by a strain gage cemented at the crack tip of each specimen. Based on the diagram of the dynamic strain history, the impact fracture toughness K(I,IC) was evaluated. The results showed that K(I,IC) of a small specimen was lower than that of a large one, and that it decreased with increasing impact velocity. When the specimen was partially supported by a notched wall, K(I,IC) increased, except for the S-type specimen. At low temperature, K(I,IC) increased for all specimens. A dense distribution of parabola patterns was observed on the fractured surface of L-type specimens.