The objective of this study is to investigate and compare the interfacial stresses between glass-fiber reinforced polymer (GFRP) composite rebar and concrete under axial loading. Rebars of three different cross-sections are considered: circular one and circular with two and four longitudinal ribs. The design analyses of the rebar configurations embedded in concrete are investigated by the 3D finite element method (FEM) using ANSYS software. FEM results convergence was examined with different FE mesh sizes comparing the calculated stresses. The influence of rib geometry on the operating stresses was also studied. The results of the interfacial stresses calculated are applied as a basis for estimation of the effectiveness of composite rebar configurations in concrete structures, which can provide good bond characteristics.