Monitoring the spatio-temporal characteristics of blood flow (BF) is crucial for physiological studies. At present, most optical techniques used for monitoring the BF utilize either the Doppler effect or the temporal statistics of time-varying speckle to measure the blood velocity at a point. If a map of blood velocity distribution is required, some form of scanning must be introduced, thus limiting the temporal and spatial resolution. Laser speckle imaging (LSI) technique could provide real-time spatially resolved BF images without the need for scanning by utilizing the spatial statistics of time-integrated speckle. In present paper, the regional blood flows in the rat mesentery under the effect of phentolamine with incremental concentration were monitored using LSI method. Our results showed that for arterioles, the vessels expanded and BF increased under the treatment with phentolamine of 1μg/ml. However, as the concentration increased, the BF decreased and dilation only happened at the concentration of 100μg/ml; For venules, no dilation was observed except for the case of 100μg/ml while BF decreased. These suggested that compared with the conventional methods, LSI could obtain the spatio-temporal dynamic of BF in the mesentery with high resolution without scan, providing a new approach in studying the microcirculation in the mesentery.