An experimental study was performed to investigate the effect of seawater exposure on the mechanical behavior of concrete columns reinforced longitudinally with glass fiber reinforced polymer (CCR-GFRP) bars. Numerous salt crystals emerged and slight exfoliation was observed after the surfaces of the columns were immersed in seawater for 120 days. The CCR-GFRP failed in either the axial compressive failure or split-crack failure mode. Furthermore, the probability of split-crack failure gradually increased with the duration of seawater exposure. In general, the carrying capacity of the CCR-GFRP initially increased and then decreased as the seawater exposure progressed. The strains of the surface concrete and inner glass fiber reinforced polymer bars continuously increased, but the strain of the glass fiber reinforced polymer bars and probability of the variability of the strain were less than those of the surface concrete. In addition, the bonding between the glass fiber reinforced polymer bars and concrete gradually decreased with increasing diameter of the glass fiber reinforced polymer bars. As the exposure period increased, the bonding between the glass fiber reinforced polymer bars of the same concrete columns weakened significantly.