As a quasi-brittle material, bamboo scrimber exhibits size effect behaviour. In this study, we used the boundary effect model to conduct a three-point bending transverse fracture test on bamboo scrimber samples with geometric similarity and dissimilarity. This test was conducted to investigate the impact of the size effect on the fracture parameters of bamboo scrimber: tensile strength ft and fracture toughness KIC. Normal distribution, Weibull distribution, and lognormal distribution were used to analyse the test data. Normal distribution was selected to predict ft and KIC values owing to its high accuracy and reliability. Then, ft and KIC were determined as the mean values of normal distribution analysis with 96% reliability. The ft value predicted was in good agreement with the ideal tensile strength obtained using the tensile strength and volume fraction of fibre bundles. Furthermore, the results showed that the ft value obtained using the BEM was unaffected by the size effect in both geometrically similar and dissimilar samples because ft is an intrinsic material property that is not affected by material defects. Because the BEM solution is size-effect independent and is a straight line that passes through the zero point, it can be used to predict the bearing capacity of large structures of bamboo scrimber using the common size samples in the laboratory.