<p>The optimal stress-controlled design of a functionally graded hollow cylinder is discovered by biomimicking bamboo, which is a “natural functionally graded material” that exhibits self-adaptive properties. In this study, we developed optimal designs of fibers that could minimize circumferential bending stress based on the morphology of bamboo. Circumferential bending stress is the dominant cause of longitudinal splitting, which is the main failure mode for both bamboo and fiber composites under bending. We formulated the circumferential bending stress equation and identified the optimal distribution that minimized stress. The result suggests that the optimal distribution to minimize stress is to change from the parabolic to the linear gradation with increasing average volume fraction. The theoretically derived optimal fiber distribution was compared with the vascular bundle distribution of bamboo. The comparison shows that bamboo cleverly distributes the vascular bundles to minimize the circumferential bending stress on the inner surface of the cross-section throughout the culm. As cracks occur first on the inner surface, bamboo can control its vascular bundle distribution across the cross-section based on regions that are highly prone to failure. In this study, the optimal stress-controlled design for hollow-cylindrical-fiber-reinforced composites is obtained, allowing us to realize the naturally optimized fiber distribution of bamboo.</p>