The authors applied an ultra-high-speed video camera to visualize crack propagation in brittle bodies, such as mortar specimens, under the impact splitting test. Strain of the brittle bodies in impact splitting tests was analyzed by means of PIV (Particle Image Velocimtery), which is usually used for measurements of flow fields with tracer particles. The results show that, when the applied impulse on the mortar specimens is increased, the crack propagation velocity reaches an upper bound. The upper bound of the crack propagation velocity was 2.6 km/sec. The horizontal tensile strain around the crack tip was estimated to be 370 mu by PIV measurement with the ultra-high-speed camera, and 270 375 mu by strain gages, respectively. Those results showed a good agreement with each other.