The flexural performance of an RC beam can be improved using the near-surface mounted (NSM) FRP strengthening technique. In such FRP-strengthened RC beams, debonding failure at the two bar ends may occur due to high interaction forces in the bar-end regions between the RC beam and the FRP bars. This paper presents a theoretical investigation into these interaction forces in RC beams strengthened with NSM FRP rectangular bars. By introducing and defining two interfacial stiffness parameters, an analytical solution for the tangential and the normal interaction forces is first obtained as an extension of the analytical solution developed by Smith and Teng  for beams strengthened with an externally bonded plate. The accuracy of the analytical solution is verified with predictions from a 3-D linear elastic finite element model.