We have demonstrated a capability of biomechanical characterization by photoacoustic measurement using various concentraiton gelatins as tissue pahntom. We have also evaluated the viscoelasticity of the cartilages tissue-engineered under the different culture conditions. Structural tissues, such as cartilage, bone, tendon, and muscle require time-dependent mechanical responses (viscoelastic properties) to describe their mechanical behavior. However, non-invasive measurement of tissue viscoelastic has not been developed; such measurement is necessary for tissue engineering applications on weight-bearing tissues. As tissue viscoelasticity affects the propagation and attenuation of the stress waves generated in the tissue, their relaxation times which are defined as the time for the stress wave amplitude to decrease by a factor of 1/e, give the viscosity-elasticity ratio of the tissue. In this study, stress waves (photoacoustic waves) which were induced by 250-nm, 6-ns, light pulses from an OPO were detected by a piezoelectric transducer. The relaxation time of the photoacoustic wave was measured for various concentrations of gelatins which had been measured their viscoelastic properties by a conventional method. Consequently, the relaxation time corresponded to the known viscosity-elasticity ratio of the gelatins. For the tissue-engineered cartileges, photoacoustic measurements were performed under the different cultured conditions. The relaxation time of the cartilages closely correlated with the viscosity-elasticity ratio measured by a convetional method. Therefore, the photoacoustic measurement is one of the qualified candidates for a non-invasive viscoelastic measurement of tissue.