This paper proposes a new methodology for determining stiffness and degradation of stiffness at the interface between externally bonded carbon-fibre-reinforced polymer (CFRP) and structural concrete under cyclic shear loading. In this paper an experimental programme consisting of 14 push-off specimens has been conducted. The CFRP composite strips were used to strengthen concrete externally at a known failure plane to resist shear stresses in shear friction. The test set-up and supports were designed such that there is a direct shear at the CFRP-to-concrete interface. This paper describes the experimental set-up and test parameters. Experimental results for cyclic bond stress-slip behaviour, mathematical formulations for stiffness of interface and its degradation as the number of cycles increased have been obtained and discussed.