Wheelchair users, such as individuals with spinal cord injuries and the elderly, have a high risk of pressure ulcer formation due to many hours a day spent sitting. To prevent pressure ulcer formation, its risk needs to be quantified. In cases of deep tissue injury (DTI), it is difficult to predict where tissue breakdown will occur as it is initiated from the tissues under the skin. Therefore, the aim of this study is to develop a human buttock dummy with force sensors and soft material to evaluate the risk of DTI due to the surface of seat. To choose the soft material of the buttock dummy, the elasticity of the human buttock tissue was measured. The proposed buttock dummy consists of rigid simulated pelvis model and simulated soft tissue made from silicone rubber. To evaluate the developed buttock dummy, the pressure force distribution of the buttock dummy was measured and compared with the sitting human, we confirmed that the buttock dummy is similar to the features of the human buttock.