Bamboo and engineered bamboo products have gathered increasing scientific and technological interests for its promising applications in sustainable engineering purpose. Bamboo-based fiber composites, a main example of engineered bamboo products, is fabricated from processing the raw bamboo bundles treated with water-soluble resin into a bamboo fiber reinforced bio-composite. The present work investigates the transverse mode-I fracture criterion of bamboo-based fiber composites: the tensile strength f t and fracture toughness K IC . The fiber bundles are taken as the “aggregates” of this material, and the average grain size G is determined as 0.4 mm. By the experimental curve between the applied load and the mid-span deflection from the three-point-bending test on single edge notched specimens, the fracture process as well as the crack development includes three stages: linear, softening and failure stages. The quasi-brittle fracture criterion is calculated with the experimental peak load P max according to the boundary effect model in non-linear elastic fracture mechanics. Also, the normal distribution analysis is applied to cover all the experimental scatters with desired reliability. Furthermore, the method in this work on bamboo-based fiber composites can be extended to study other fiber reinforced composites.