Abstract: All bamboo species of Phyllostachys belong to the perennial monocarpic plants. They flower only once through their lives. After flowering, the vegetative mass dies out naturally. The opinions concerning the flowering of bamboos may fall into fwo major categories: the external cause theory and the periodicity theory. The former insists that the flowering of bamboos is due to the external factors such as climat, nutrition, pest and silvicultural practices etc. The latter asserts that the internal physiological calender, controlcd by "biological clock" and buffered from environmental impact very well, is responsible for the flowering of bamboos. Synchronous flowering of bamboo clones growing at diverse habitants enables the periodicity theory to dominate the others. Generally, the periodical interval of flowering of most species in Phyllosiachys varied from 20 to above 100 years. The instability of the period of flowering can be explained by gene mutation and natural rejuvanation. Phytohormones such as IAA, ABA and GAs may be involved in the flowering affairs of bamboos, but their concrete roles remain uncertain.