Abstract Yukwa, a Korean oil-puffed rice snack with a soft texture, is currently being manufactured primarily by traditional methods. The water-steeping time of the milled waxy rice is an important factor because it has a great effect on the product quality. The expansion rates related to water-steeping durations, which are indices of Yukwa quality, were quantitatively evaluated using image analysis. The longer the water-steeping time was, the higher were the expansion parameters of the Yukwa. When the waxy rice was water-soaked over 6 days, the expansion rate of the Yukwa showed a statistically significant increase. Using these expansion rates, the diameter and diameter-implicit parameters were statistically modeled with respect to the moisture content of the rice at P leqslant R: less-than-or-eq, slant 0.01. Hedonic sensory evaluation for Yukwa showed that the longer raw waxy rice was water-steeped. The better quality was due to high expansion.