Identifying the parameters of an assumed transfer function using the relay feedback control has become an accepted practical procedure. In process control problems, the transfer function may involve an integrator. Therefore, in this paper, a modified relay feedback control for parameter estimation of an integrating plus first-order plus dead time (IFOPDT) plant transfer function has been suggested, using the A-Function method, which is an exact method for investigating a limit cycle to occur. The effect of static load disturbances has been included in the derived expressions for a limit cycle to occur, so that better estimations can be performed under static load disturbances.