A method for establishing second order plus dead time model parameters under closed-loop PI control is proposed and its performance compared with the recent method of Park et al.(1). It can be readily applied regardless of whether the response obtained during closed-loop identification is under-or over-damped. The drawbacks of the other methods in existence, i.e., poorer model fit due to first order plus dead time approximation and or the need for a step test under P-control, are overcome. The required closed-loop response data can be obtained while the process is in normal operation since many industrial controllers are of the PI-type. Simulation results reveal that the proposed method produces reliable parameter estimates and its accuracy is comparable with the method of Park et al.(1). The relative advantages of both these methods are discussed.