This paper reports on part of an ongoing experimental program at The University of Adelaide on the seismic behavior of high-strength concrete (HSC)-filled fiber reinforced polymer (FRP) tubes (HSCFFTs). The results from three square concrete-filled FRP tube (CFFT) columns that were tested under combined constant axial compression and reversed-cyclic lateral loading are presented. The main parameters of the experimental study included the axial load level, concrete strength, and FRP tube corner radius. The results indicate that square HSCFFT columns are capable of developing very high inelastic deformation capacities under simulated seismic loading. The results also indicate that increasing the corner radius beyond a certain threshold value provides no increase in column lateral drift capacities. It was observed that column deformability decreased with an increase in axial load level (P/Po) and concrete compressive strength (fc). The results of the experimental program are presented together with a discussion on the influence of the main parameters on the seismic behavior of CFFT columns.