Human joints are subjected to dynamic or impact loading in life. However, conventional biomechanical research of human joints has been concerned principally with static loading condition. The purpose of this study is to investigate the mechanism of load transmission in knee joint under impact loading condition. In experiment with drop-tower impact apparatus using porcine knee joint, compressive stresses transmitted from femur to tibia through the knee joint were measured using small compresslye stress sensor inserted in cancellous bone. According to the experiment, a compresslye stress caused by impact load is much higher than a stress by static load. And an impact stress in the media1 side is higher than the one in the lateral side in knee joint.