Thorax plays a crucial role in shielding internal organs from external loads. To establish a rational safety criterion for traffic accidents, it is important that we understand the mechanical behaviors of the thorax. We studied the response of thorax to impact experimentally. The purpose of this study is to understand the characterization of thoracic structure from measurement parameters by impact test. The specimen used was porcine thorax, the size of which was approximately equal to human thorax, after removing the internal organs. Using original test apparatus, the specimen was subjected to low energy impact and a sensitivity study was conducted to explore various parameters, including the response to the impact load, strain on each rib, and the acceleration and displacement in the thorax. Comparison of impact locations (front, back, and lateral) showed characteristic variations among the results. A frontal impact produced large acceleration and displacement. Therefore, it could be expected to stress the internal organs directly. In the case of an impact from behind, the impact response load was higher and the deformation of thorax was remarkably small. It appeared that the thoracic resists backward impact, and provides protection of internal organs. In lateral impact, the concentrated load tends to occur in the ribs, and the rib strain was high. Hence, the rib parts were prone to fracture, and the internal organs were subject to increased risk of secondary damages of the bone fracture due to bone sticking organs. In conjunction with the impact tests, static compressive tests were conducted. The deformation behavior of the thorax is grossly affected by the constraints of the binding of ligaments connecting bones. Therefore, this structure provides smooth elasticity by transforming the whole structure when a load is applied to the thoracic parts. This provided confirmation of the structural characteristics that were obvious in impact testing. This is the first time that attention has been paid to the thoracic structure and its deformation behavior has been investigated. The response of thoracic structures to external loads requires further research. © 2008, The Japan Society of Mechanical Engineers. All rights reserved.