A new theoretical model to evaluate the moment-rotation (M-) elationship for stiffened and extended steel beam-column end-plate connections has been derived in this paper. Based on a specific definition of the end-plate connection rotation, the end-plate connection is decomposed into several components, including the panel zone, bolt, end-plate and column flange. The complete loading-deformation process of each component is then analysed. Finally the loading–deformation process for the whole connection is obtained by superimposing the behaviour of each component. In addition, 5 joint tests have been conducted to verify the proposed analytical model. By comparing it with the test results, it has been concluded that this analytical model can evaluate the rotational behaviour of end-plate connections, as well as the moment-rotation (M-) curve and the initial rotational stiffness accurately. Furthermore, it can analyse every contribution to the joint's rotational deformation, such as the shear deformation of the panel zone, the bolt extension, the bending deformation of the end-plate and column flange, etc. This analytical model also provides moment-shear rotation (M-s) and moment-gap rotation (M-ep) curves, which establish a reliable foundation for analysing the detailed rotational behaviour of end-plate connections.