Starches, widely used by the food industry, are generally insoluble in water at room temperature before going through the gelatinization process, which involves heating the crystalline polymer granules so that their solubilization occurs. The temperature at which gelatinization takes place varies for each type of starch, depending on the source of origin and/or modification process. Therefore, this study proposed to observe the diameter of the granules to identify the gelatinization temperatures of different types of starches through images obtained through optical microscopy. The starches used with their source of origin and commercialization were cationic starch - corn (Foxhead 5804), anionic 1 (Superion 3050) and anionic 2 (Horizonte HC 50) - cassava, and nonionic – potato. They were heated in water under constant agitation. When system temperatures reached 40 ºC, aliquots were removed at time ranges of 10 ºC in the range 40 - 90 ºC and characterized by optical microscopy under normal light with images recorded at 100x magnification. The diameter of the granules was evaluated through the images using the ImageJ® software. It was observed that the granules of starches dispersed in water had different sizes as a function of temperature and the variety of starch. The nonionic starch granules had a considerable increase in diameter from 70 °C onwards. Upon reaching 90 °C, most of the granules disintegrated. This being a typical behavior of native (unmodified) starches. The granule swelling behavior found for cationic starch was similar to that observed for nonionic starch. Anionic starches showed no difference between granule sizes with increasing temperature. This can be associated with a chemical modification that alters the characteristics of the granules. Finally, it can be observed that the images performed by optical microscopy can be used to evaluate the gelatinization process of starches.