Laboratory experiments and numerical simulations, using Particle Flow Code (PFC3D), were performed to study the behavior of jointed blocks of model material under uniaxial loading. The fracture tensor component in a given direction is used to quantify the combined directional effect of joint geometry parameters including joint density, orientation and size distributions, and the number of joint sets. Both the laboratory experiments and the numerical simulations showed that the uniaxial block strength decreases in a nonlinear manner with increasing values of the fracture tensor component. Joint geometry configuration was also observed to control the mode of failure of the jointed blocks and three modes of failure were identified, namely (a) tensile splitting through the intact material, (b) either only shear failure along the joint planes or both shear and tensile failure with respect to the joint planes and, (c) mixed mode failure involving both the failure mechanisms in (a) and (b). It has also been shown that with very careful parameter calibration procedures, PFC3D could be used to model the strength behavior of jointed blocks of rock under uniaxial loading.