In this paper we present an improved bi-material beam theory with adhesive interface, which has been applied to the study of the interfacial behavior in a concrete beam reinforced by an externally bonded fibre reinforced polymer (FRP) plate. The work explicitly considers the interfacial slip effect on the structural performance by including the effect of adherend shear deformations. This new method needs only one differential equation to determine both shear and normal interfacial stress whereas the others solutions in the literature need two differential equations. Compared with previously published analytical results, this one improves the accuracy of predicting the interfacial stresses and the solution is in a closed form. This research is helpful in the understanding of the mechanical behavior of the interface and design of FRP-reinforced concrete (RC) hybrid beams. (C) Koninklijke Brill NV, Leiden, 2011