The asymmetrical relay feedback method is modified to get improved parameters estimates of a first order plus time delay transfer function model. The method uses a single relay test. Analytical solution is provided for the model parameters. The method overcomes the problem of getting a negative time constant by the conventional symmetrical relay testing for modeling higher order system. Simulation results are given for stable and unstable transfer function models. The proposed method gives model parameters close to the actual values and gives closed loop ISE values similar to that of the actual system. The method is also compared with that of Huang et al. (AIChE J., 42 (1996) 2687) and Shen et al. (AIChE J., 42 (1996) 1174).