Abstract: Experimental study for a set of endplate-connections of rectangular hollow steel columns and I-type beams which are widely used in engineering are put forward.The practical situation that the circular opening is set at one side of the rectangular hollow steel column are considered for the tests.The openings are usually called hand-opening which are for convience of the bolts being installed.Through the experiments,the stiffness of connections and its variation,bearing capacity of moment of the connection and the curves of moment-rotation are all obtained,which can be used as basis of practical design of the connections.The experimental results show that the rotational stiffness of the endplate connections greatly vary for different constructional parameters of the joints,which tell us the important facts that all the endplate connections are considered as rigid connections in practical design is not proper.