Abstract As flax fibers exhibit good mechanical properties and low cost, they are considered as efficient renewable reinforcement of polymers. The fiber properties are now relatively well-known, but information about the mechanical behavior of the interfaces between fibers of a bundle is still missing, whereas it is of crucial importance when modeling the deformation of the derived composites. In this study, the shearing properties of a pair of elementary fibers are experimentally determined to characterize the behavior of the fiber/fiber interface. A cohesive zone model is chosen and its parameters are identified. A numerical model with a pair of fibers is developed to estimate the shear behavior of the fiber/fiber interface. The corresponding stress-displacement curve shows a good agreement between the maximum shear strength obtained by simulation and the experimental value. Moreover, the progressive damage of the interface is well reproduced although the shear curves are not linear, contrarily to the experimental observations.