Abstract: Sound transfer functions of bones are measured in vivo and in vitro with two accelerometers. Experimental results show that bones have sound low-pass filtering property, and can vibrate in several modes. Characteristics of sound transfer function vary with individual, but data obtained in left and corresponding right limb of the same test object are comparable. The resonant frequency of sound transfer function can indicate the size of defect in bone well, so it can be used for diagnosis of bone disease and assessment of fracture healing.