ABSTRACT: Starch granule microstructure affects the digestion of starch and its nutritional impact; however, the exact relationship between both factors is not clear. This study reports quantitative relationships between granule size (length and polygonal area), degree of gelatinization (DG), in vitro digestibility (by enzymatic methods), and glycemic response of potato starch granules gelatinized to various extents by heating at several constant temperatures in the range of 55 to 65 °C. DG measured by differential scanning calorimetry was closely related with heating temperature (R2= 0.997), size parameters of granules (measured by image analysis), in vitro digestion, and in vivo glycemic response (R2 of adjusted models > 0.9); shape parameters of granules (measured by image analysis) were not related with DG. Results demonstrate that DG of starch strongly affects its digestibility in vitro, and may influence the postpandrial glycemic response. Future studies should be performed to investigate the effect of potato starch gelatinization on the nutritional impact at other temperatures and in more complex matrices.