We simulate rock fracture using ESyS_Particle, which is a 3‐D Discrete Element Model developed for modeling geological materials. Two types of simulations are carried out: Unconfined Compressive Test (UCT) and Brazilian Tensile Test (BTT). The results are compared to laboratory tests. Model parameters are determined on the basis of theoretical studies on the elastic properties of regular lattices and dimensionless analysis. The fracture patterns and realistic macroscopic strength are well reproduced. Also the ratio of the macroscopic strength of compression to the tensile strength is obtained numerically.