This paper is concerned with the technique of identifying a non-linear electromagnetic system experimentally based on the principle of harmonic balance and the curve fitting method. The system under investigation is a symmetric rotor suspended by a spring device and excited by an electromagnet of a magnetic bearing. Particular emphases are placed on the identifiability of such a technique for this system and how to improve the modelling accuracy. The traditional identification technique is modified in order to successfully identify this system possessing highly non-linear characteristics. The resulting non-linear model has been proven to be in agreement with the experimental data. The knowledge gained from these studies are presented and discussed thoroughly. (C) 1998 Academic Press.