The application of composite rebars instead of steel ones offers good corrosion resistance and durability. Composite rebars with different shape have been proposed (Kadioglu, 2005), but their influence on bond strength with concrete does not investigated in details. The objective of this study is to investigate and compare the interfacial stresses arising 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 3D finite element method (FEM) using ANSYS software. FEM results convergence was examined with different FE mesh sizes and comparing the calculated stresses. Influence of rib geometry on the operating stresses was also studied. The results of 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.