Based on the principle of total internal reflection, a new experimental system , in which the sample is close sandwiched between two prisms, was designed to determine the refractive indices of biotissues and homogeneous medium. Some mammalian tissues have been determined at laser wavelengths ofO.488, 0.6328, 1.0795 and 1.3414?tm, respectively, and their dispersion equations have been obtained. And the absolute error between the n calculated from the dispersion equation and the measured is within 0.002. By utilizing these dispersion equations, the refractive indices of the tissues can be obtained at any wavelength within the waveband of O.488-1.3414?m. The method has great reliability and accuracy, and it can be used for measuring the refractive indices of biotissues and any other medium.