The application of recycled aggregate concrete (RAC) has so far mainly been limited to nonstructural components because of its inferior short- and long-term performance compared with normal concrete. Encasement of RAC with a fiber-reinforced polymer (FRP) tube has been demonstrated to be an effective technique to improve both the mechanical properties and durability of RAC. A number of studies have been carried out on FRP-confined RAC in circular columns. However, only a limited number of studies have examined the behavior of FRP-confined RAC in rectangular columns, and the existing test specimens were all small-scale. Existing studies have shown that there may exist a significant behavioral difference between small- and large-scale FRP-confined rectangular concrete columns (i.e., column size effect). Against this background, a first-ever experimental study on glass FRP (GFRP)-confined square RAC columns of three different sectional widths ranging from 200 to 400 mm was conducted and the results are presented in this paper. The same FRP confinement stiffness was adopted for the columns of different sizes so that the possible column size effect could be examined. The test results showed that the size effect indeed existed in the test FRP-confined square RAC columns and the presence of recycled aggregate amplified such effect. The size effect should be considered in the design of such columns especially when the coarse aggregate replacement ratio is relatively large. The accuracies of three existing strength models for FRP-confined normal concrete in square columns were also evaluated using the test results.