This paper proposes a fuzzy adaptive control approach based on a modular design for uncertain chaotic Duffing oscillators. Using fuzzy logic, the unknown nonlinear function in the Duffing oscillator is approximated. Subsequently, a modular adaptive controller is derived consisting of an input-to-state stabilizing (ISS) control module and a passive identifier module. Since the modular design allows for independent design of the controller and identifier, the proposed method provides substantial flexibility in the choice of a parameter identifier. Additionally, the modularity of the controller-identifier pair provides simplicity in the control system derivation. Simulation results are included to illustrate the effectiveness of the proposed approach.