We studied the mechanism by which gibberellin A3 (GA) inhibits the growth of aerial tubers (ATs) in the Chinese yams (Dioscorea oppositifolia) 'Nagaimo' and 'Ichoimo.' Specifically, we examined the morphological changes that occurred during the differentiation and growth of ATs in the axillary buds of GA3-treated shoots that were grown upside down and known as reverse treatment (RT). Prior to RT, each axillary bud produced a main bud and 1 or 2 accessory buds in both cultivars. 'Nagaimo' produced a dome-shaped protrusion at the base of the main bud. These dome-shaped protrusions were located at axillary buds of the first to fourth unfolded leaves. We hypothesized that this dome-shaped protrusion would develop ATs in response to a tuberization stimulus, such as RT. On the other hand, 'Ichoimo' did not develop these dome-shaped protrusions at the axillary buds of the primary to fourth unfolded leaf. After 15 days of RT, the dome-shaped protrusions that arose from the axils in the first to eighth unfolded leaves and in the first to fourth folded leaves in the 'Nagaimo' cultivar rapidly developed AT morphology. However, since the buds on the other axils aborted, these axils only produced one main bud or one main bud and one accessory bud. After 45 days of RT, effect of GA on morphological changes during the differentiation and growth of aerial tubers was observed in both cultivars. As the result, the control plants of both cultivars developed large ATs, whereas the GA-treated plants produced very few ATs since almost of the accessory bud had aborted at the base of the main bud. Therefore, axillary buds (almost accessory bud) in Chinese yams are most sensitive to tuberization stimuli between the first and eighth unfolded leaves. However, GA inhibited AT production by either aborting buds before differentiation or suppressing the differentiation of buds producing ATs.