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The purpose of this research was to develop a pulsed wave Doppler ultrasonic measuring system for the quantitative investigation and determination of the elasticity and viscosity of living soft tissue. A pilot study of the tissue-like gel phantom was applied for investigating the feasibility of the system. Theories in continuum mechanics, viscoelastic biosolids, wave propagation, Doppler ultrasound, communication and digital signal processing form the basis to provide underlying principles for the development of this research. In the viscoelasticity model, a low-frequency and small-amplitude vibrator was designed to facilitate shear wave propagation through the tissue-like medium due to the incompressibility. The amplitude and phase of displacement were analyzed from the spectrum of demodulated Doppler signals. The elasticity and viscosity are then derived and estimated from the amplitude and phase gradients of tissue displacement. The results by pulsed wave Doppler ultrasonic measuring show that the elastic modulus and viscosity for each gel phantom are increasing with an increasing frequency, and the energy loss of middle gel phantom is increasing with an increasing frequency.