Abstract: Size effect is a popular and difficult issue in the field of rock mechanics. In this paper, the uniaxial compressive strength of marble, diorite and tuffsamples with the maximum sample size 400 mm×400 mm×800 mm were tested using the self-developed large-scale rigid testing machine. Two cases of size effect of rock uniaxial compression strength were conducted:one is with the same aspect ratio and the other is different aspect ratio with the same length and width. The results show that, with the increase of samples dimensions, the uniaxial compression strength decrease in logarithmic function form and gradually approach to a certain value in the case that with the same aspect ratio; In the case that with different aspect ratios, the length and width of the samples are 200 mm×200 mm, and the heights are 200 mm, 400 mm, 600 mm and 800 mm respectively. The uniaxial compression strength decreased first and then increased as the increase of aspect ratio of samples. And the corresponding failure modes of samples are complex splitting, splitting and shear failure respectively as the increase of aspect ratio. The results of uniaxial compression strength of different dimensions presented in this paper provide the basic data for the size effect research of rock samples. At the same time, the results have some reference value for the correction of size effect in the practical engineering.