The Particle Flow Code (PFC), a numerical simulation code based on the distinct element method, is a useful tool for simulating the failure behavior of hard rocks. The introduction of clump logic (Cho et al., 2007) into the PFC modeling has made it possible for us to better reproduce the brittleness characteristic of hard rocks, namely, the large difference between compressive strength and tensile strength. However, there is a problem in the PFC simulation with the clumped particle model, namely, when we simulate Brazilian tensile tests on hard rocks, the results do not fully express the rapid decrease in tensile stress after the peak stress. One reason for this problem is the existence of clumps that block the rapid propagation and the connection of the micro-cracks in the model by their interlocking effect. Focusing on the effect of clump configuration on the Brazilian tensile failure behavior of hard rocks, this paper carried out simulations by varying clump size and ball size. The experimental mechanical properties of Lac du Bonnet granite (Potyondy and Cundall, 2004) were targeted in the simulations. From the simulation results, we confirmed that brittleness can be controlled by changing the ratio of clump size to minimum ball size and that under a constant ratio of clump size to minimum ball size, the local peak stress does not change with the minimum ball size.