Poisson’s ratio is defined as the negative value of the ratio of the radial strain and the corresponding axial strain, caused by uniformly distributed axial stress, within the scope of the material’s proportional limits. It reflects the lateral deformation of the material, and is widely used in elastic theory. Previous studies have shown that the upper and lower limits of Poisson’s ratio are 0.5 and -1, respectively, and Poisson’s ratio for the vast majority of materials is 1/3 (Lakes 1987; Shan et al. 2006). In the field of numerical analysis of geotechnical engineering and engineering design, Poisson’s ratio is an important parameter reflecting the lateral deformation of the rock and soil mass and it directly affects the strength and deformation characteristics of the rock and soil mass. According to Code for rock tests of hydroelectric and water conservancy engineering (Code DL/T 5368-2007), the Poisson’s ratio of rock material should be determined by uniaxial compression tests. Adopting this method, resistance strain gauges should be pasted onto the surface of standard samples to obtain the lateral and axial strains, and then the Poisson’s ratio can be obtained by the related formula. However, there are shortcomings to this method (Lau et al. 2004; You 2007; Zhou et al. 2007): (1) strain gauges can only measure the partial deformation of the rock sample and cannot represent the overall deformation properties of the sample; furthermore, the quality and direction of pasting and other factors will affect the measurement accuracy. (2) Under a uniaxial compression condition, the lateral strain of the rock accrues earlier, and then deviates faster from the linear relationship with the axial stress than the axial strain, which leads to a nonlinear relationship compared with the definition of Poisson’s ratio. (3) Most engineering rock mass experiences mechanical excavation and unloading processes, which are different from the loading process required by the specification. Based on the generalized Hooke’s law, we propose a method for determining the Poisson’s ratio of rock samples by changing the axial stress and unloading the lateral stress. By unloading axial and lateral stress triaxial tests (UAUL) and loading axial stress and unloading lateral X. Xu (&) R. Huang H. Li Q. Huang State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu, Sichuan 610059, China e-mail: xtxu@cdut.edu.cn