Abstract-In this paper, dielectric characteristics of female breast tissues were measured. Breast Tissues were mainly composed of fat, fibro-glandular and tumor. Measured tissues were directly extracted from mice and a rat just before the measurements to maintain the tissues as fresh as living ones before degeneration. This makes the measured results more accurate. Because the extracted tissues were very thin, they were measured by two methods using HP probe and a newly designed two-port sample holder. Numerical results for the twoport sample holder were obtained for both the forward and inverse problems. Dielectric properties of breast tissues were measured in the frequency range between 50 MHz and 5 GHz. We calculated the electrical constant with the measured data from the two-port sample holder. As a result of the measurement, the dispersion characteristics of the female breast tissues were fitted into the first Cole-Cole model.