Abstract: Based on 18 beam tests, 42 Losberg pullout tests, and 6 standard pullout tests, the constitutive relationship of bond-slip behavior for GFRP rebars in concrete is systematically analyzed. The experimental bond stress-slip (τ-S) curves of sand-coated deformed GFRP rebars in concrete are composed of four segments, i.e. micro-slippage segment, slippage segment, descending segment, and residual segment. The four segments are divided by elastic bond point, peak bond point, and residual bond point, respectively. It has 3 major differences from deformed steel rebars, 1) the ascending segment of τ-S curves of GFRP rebars is subdivided into the micro-slippage segment and the slippage segment; 2) smaller drop of the bond stress occurs in the descending segment; 3) the curve in the residual segment is approximately sinusoid. With the increasing of the embedment length and the diameter of GFRP rebars, the slippage at the peak bond point, as well as the bond stresses at three characteristic points, decrease. This paper also develops the theoretical model for the bond-slip relationship of GFRP rebars in concrete, the theoretical formulae of bond stresses, and the corresponding slippages at the characteristic points in τ-S curves.