This paper presents a decentralized fuzzy control problem for asymptotic stabilization of a class of nonlinear large-scale systems that use an observer-based output-feedback scheme. A Takagi-Sugeno (T-S) fuzzy model is adopted for the nonlinear large-scale system, which has unknown interconnection terms, and a fuzzy controller is separately considered for measurable and nonmeasurable premise variable cases. Sufficient conditions are derived for both asymptotic stabilization and optimization of a maximum bound of interconnection and are formulated in terms of linear matrix inequalities. Finally, numerical examples are provided to verify the effectiveness of the proposed techniques.