Abstract This paper presents a new explanation of the mechanism of anther dehiscence in rice during the period from floret opening to pollen dispersal. The theca dehisced on the stomium in the apical part and the anther wall in the basal part of the large locule. Comparison of the anther dehiscence process under various air humidity conditions showed that the process, until the splitting at the apical and basal parts, was a moisture-requiring process whereas the widening of the splits in both parts was a desiccatory process. Observation of the anther transverse section, revealed the marked development of the U-shaped thick cell wall in the endothecium adjacent to these two splits. From these observations, the anther dehiscence mechanism may be explained as follows. At the time of anthesis, pollen grains swell rapidly in response to the floret opening and cause the theca to bulge, rupturing the septum. The pollen pressure combined with the inward bending of the locule walls adjacent to the stomium causes splitting of the stomium in the apical part of the theca. At the same time, the septum rupture extends to the bottom of the large locule supported by the pollen pressure. After these processes, the locule walls adjacent to both splits straighten probably due to their water loss. This straightening widens the splits and the swollen pollen grains overflow from the widened splits.