Bamboo is a unique unidirectional biocomposite, which consists of vascular bundles (VBs) as the reinforcement and parenchyma cells (PCs) as the matrix. The non-uniform distribution of VBs embedded in the matrix makes bamboo a functionally graded material. In order to investigate the compressive behavior of bamboo as a function of its components, compression tests were performed on specific bamboo samples with different VB volume fraction (V (vb)), collected from different positions in the culm wall. The results show that both compressive strength and modulus increased linearly with V (vb), while the plastic deformation of samples in the compression decreased with increasing V (vb). This indicates that VBs dominate the compressive strength and modulus of bamboo, while the ductile performance of the bamboo is determined by the foam-like PCs. Scanning electron microscope observation indicated that VBs buckling were the main cause of failure. The Euler theory was applied to investigate the buckling behavior of bamboo blocks, showing that theoretical buckling strength when only considering the effect of VBs was much lower than with the test results, with the theoretical buckling strength being closer to test results when considering both the effect of VBs and PCs. It is therefore necessary to consider the contribution of PCs to resist buckling in bamboo, as their foam-like structure can effectively prevent the large-scale buckling of VBs.