Time-temperature profiles of model starch water-systems, containing 0-35 % of water were studied, under microwave irradiation and effect of this treatment on physico-chemical properties of starch were recognized. Brabender rheological method, light microscopy, scanning electron microscopy and X-ray diffractometry were involved. Microwave irradiated starch containing more than 20 % of water underwent isothermal structural transformation. Consequently gelatinisation temperature rose and starch partially lost its solubility in water. The most dramatic change took place in case of potato starch. Its crystal structure changed from B into the A type. Tapioca starch changed to a lesser extent. Both tapioca and potato starch with less than 20 % of water solely lost their humidity on short irradiation then dextrinized.