Ultrasonic imaging has become increasingly important as a diagnostic tool in medicine because it is noninvasive and it can provide valuable information otherwise unattainable. However, at present, clinical interpretation of an ultrasonic image still mostly relies on recognition of boundaries and positional relationship of anatomical structures and a subjective analysis of the distribution or texture of echo amplitudes. Other potentially useful information carried back by the echoes is completely discarded. The aim of ultrasonic tissue characterization research is to develop methods to extract additional information from the returned echoes so that tissue pathology or abnormality can be reliably identifed and severity of the pathology objectively assessed with quantiative criteria. A number of ultrasonic parameters including acoustic velocity, impedance, attentuation and scattering, have been utilized in attempting to achieve this goal. In this paper, recent progress in this research will be discussed and relevant results presented.