Starch–water suspensions were exposed to ozone gas for 1 h at 5 °C. The concentration of dissolved ozone gas in the suspension was kept at 4.2 mg ozone/L−1 water. Polarised light and scanning electron microscope (SEM) were used to examine the birefringence and surface characteristics of the samples, respectively. A differential scanning calorimeter (DSC) was used to measure the gelatinisation properties, while a rapid visco analyser (RVA) was used to examine pasting properties. The structure of corn and potato starch showed very little change after treatment with ozonated water. The DSC gelatinisation temperatures (i.e. onset, peak and conclusion) of starch samples increased as a result of ozonation. However, a decrease in gelatinisation enthalpies was observed for ozonated starch samples. A dramatic decrease in the RVA viscosities of ozonated starch samples was observed after ozonation, which are explained by the partial cleavage of the glycosidic linkages in the starch granules during ozonation.