This paper presents an approach to analyze stability robustness of fuzzy control systems (FCSs) by using H-infinity control approach. The fuzzy logic controller (FLC) is replaced by the describing function. As a consequence, a non-linear FCS is transformed to a quasi-linear control system with model uncertainty. The system obtained is then rearranged to be a two-block structure in such a way that the robust stability can be determined by implementing the small gain theorem and the existence of the limit cycle oscillation can be predicted.