Although the size of specimens presents significant effect on the mechanical performance of CFRP confined concrete columns, the size effect is a blank area of study until now. Based on a series of tests on seven groups of Carbon Fibre Reinforced Plastics (CFRP) confined large-scale square concrete columns with different corner radius, the basic mechanical properties were obtained, such as the failure modes, compressive strengths, stress-strain relationships, and the ultimate strain distribution of CFRP jacket. Moreover, their comparison with the experimental results of the smaller-scale specimens has been investigated and published. It is demonstrated that the confined strength increases with the increase of the corner radius except for the specimens with sharp corner. All of the specimens fail due to CFRP rupture, and the fracture location occurs in the chamfer zone. Meanwhile, the phenomenon of the stress concentration is obvious. The confinement ratio, i.e., MCR, shows a certain correlation with the size of specimen on the compressive strength of CFRP confined specimens. The ultimate strains measured on the CFRP jackets are about 35% less than that tested by the coupon specimens, while it is more serious than that for the smaller-scale specimens. It is found that the discrepancies between the predicted results of the existing strength models of CFRP confined square column and the experimental results in this work are obvious. It suggests that the size effect on the FRP confined square columns cannot be ignored,which needs to be further researched.