One of the authors has already defined the critical strain of rocks, which is the ratio of uniaxial strength to Young's modulus, and demonstrated that the critical strain can be used as an allowable value in assessing tunnel stability. The previous study on the critical strain has mainly been restricted to homogeneous rocks. However, we often encounter non-homogeneous rocks when a tunnel is excavated in a geologically complex ground. Thus, uniaxial and tri-axial tests were carried out in the laboratory to investigate the critical strain of non-homogeneous rocklike materials. 3-D finite element analyses were also conducted to assess the results of the experiments. In this paper, the experimental and numerical results have been presented and the characteristics of critical strains of nonhomogeneous materials have been clarified.