Parallel Strand Bamboo (PSB) is a biocomposite composed of long narrow parallel bamboo strands which are adhesively bonded under high pressure. It has more and more attractive structural applications in building and construction engineering. It’s important to well understand the stress-strain relationship to develop the constitutive law and conduct the nonlinear analysis of PSB structures. The PSB was treated as an transversely isotropic composite in the experiment and the uniaxial parameters in each main material axis and the pure shearing parameters in each main material plane were proposed, and the corresponding stress-strain relationships of each stress state were also established. The results show that compared with common used woods in construction engineering, PSB has higher strengths with less variability. Strength of tension parallel to grain is nearly as twice as that of compression parallel to grain. In perpendicular to grain direction, the strength of tension is much lower than the that of compression. Shearing in transverse-to-grain plane presents lowest modulus and strength than those shearing in other two directions. The shearing strength in perpendicular to grain is as about 3 times as that of shearing in parallel to grain direction. The stress-strain relationships and the failure modes of PSB are significantly depended on the way in which the fiber participated. In parallel to grain direction, tensile damage almost entirely contributes to the broken of fibers, which shows the highest strength and brittle behavior among all stress states. In other cases, when the expending of failure cracks are restricted by fibers, the damage presents progressive process and higher strength, and the stress-strain relationships exhibit linearity in the earliear life while turn to nonlinearity in the later life of the specimens. When damages take place in matrix or in fiber-matrix interface without fibers involved in, the material shows lower strength, and the stress-strain curves present linear and brittle behavior.