This paper proposes a novel adaptive fuzzy decentralized output-feedback control approach for a class of uncertain nonlinear large-scale systems. The considered nonlinear systems possess the unknown nonlinear functions, unmeasured states and unknown time-varying delays. Fuzzy logic systems are
employed to approximate the unknown nonlinear functions, and adaptive high-gain filters are presented to estimate the unmeasured states. Based
on the designed high-gain observer and Lyapunov-Krasovskii functionals, and using the backstepping design and dynamics surface control (DSC) approaches, a novel adaptive fuzzy tracking controller is designed. It is proved that the proposed control approach can guarantee all signals of the
closed-loop system are semi-globally uniformly ultimately bounded (SGUUB), the observer and the tracking errors converge to a small neighborhood of
the origin. Finally, the simulation results are provided to demonstrate the effectiveness of theoretical results.