In hyperthermia, blood flow plays a major role in determining the effectiveness of hyperthermia used alone or combined with radiation therapy or chemotherapy. The acidity, the nutritional supply, partial pressure of oxygen and distribution of drugs are closely related to blood flow. To facilitate these issues we put forward a simple optical method to measure dynamical change of blood volume combining laser speckle measurement and CCD microscopic imaging technique. In this study, we selected seven different temperatures (40°C, 42°C, 43°C, 44°C, 45°C, 47°C, 49°C), and monitored variations of blood velocity and diameter of microvessels (15~50μm) on BALB/c mouse’s mesentery and through tumor during 30 minutes at each temperature. The results showed that the critical temperatures of normal and tumor microvessel were 43°C and 42°C. Tumor is more thermal sensitive than normal tissue. And the capacity of tumor blood flow to increase upon heating appears to be rather limited. The increase of blood volume was not more than 2.0-fold.