Morphological changes of ramie fibers due to swelling in alkali solution were investigated. The observed twisting and changes in the cross-sectional shape of the fibers could be explained as a geometrical alteration caused by lateral expansion of coiling fibrils, as the unmercerized ramie fiber showed an S-helix structure. The fibril angle of ramie fibers was estimated to be 3°. Although the swollen fiber untwisted to some extent on washing with water, the shape of the twisted ribbons as observed by scanning electron microscopy was retained even after drying. Concentrated 8N NaOH produced only a moderate change in morphology, whereas swelling with 3.5N NaOH at 0°C expanded the cross sections about 30 times over the initial ones accompanied by a drastic change in the shape of the fiber.