Abstract: The study shows the direct relationship between the temperature field and the parallel changes that are taking place in backscattered ultrasonic signals from breast tissue in vivo when heated to temperature of approximately 42C. The non-uniform temperature field inside the tissue being heated was determined by a numerical model using FEM. It is shown that the spatial distribution in some areas of intensities of the backscattered signals coincides with the temperature distribution field predicted by the numerical model. The result indicates the possibility of indirect measurement of the temperature rise in breast tissue in vivo by measuring the intensity variations of the ultrasound echo.