The structural changes of potato starch granules, caused by hydroxy‐propylation, were studied using light microscopy. The starch samples used consisted of a native potato starch, hydroxypropyl potato starches with varying molar substitution (M. S.) and a hydroxypropyl and cross‐linked potato starch. The structural characteristics of the samples were evaluated by comparing the colour intensities of thin sections of samples stained with iodine and Schiff's reagent. The manner of loss of birefringence of samples in 5 M aqueous urea under polarized light was observed as well. The results obtained by three different methods were found to be similar to each other, suggesting that the central region of the potato starch granule is where hydroxy‐propylation mainly takes place or where hydroxypropyl groups are mainly distributed. The results can provide an explanation for the altered pasting properties of hydroxypropyl potato starches depending on their M. S.