Glycaemic variability challenges the accuracy and use of the glycaemic index (GI). The purpose of the current study was to determine the role of mastication on GI. Using a randomized, controlled, crossover, non-blind design, 15 healthy young subjects returned on 5 separate days for three glucose and two rice test sessions. At the rice sessions, subjects chewed each mouthful either 15 or 30 times. Rice chewed 15 times produced a total glycaemic response (GR; 155 mmol min/l), peak GR (2.4 mmol/l) and GI (68) significantly lower than when chewed for longer (30 times) (184 mmol min/l, 2.8 mmol/l and 88, respectively). The study shows that the GI of rice is affected by the degree of mastication. Chewing 15 times compared with 30 times significantly attenuates the GI, suggesting that mastication may potentially contribute to the glycaemic variability of rice. While future work must establish the extent and limits to which mastication affects glycaemia, it could also explore the potential of using mastication to reduce the glycaemic load of rice.