In this paper, an observer-based direct adaptive fuzzy-neural controller (ODAFNC) for an anti-lock braking system (ABS) is developed under the con-straint that only the system output, i.e., the wheel slip ratio, is measurable. The main control strategy is to force the wheel slip ratio to well track the optimal value, which may vary with the environment. The observer-based output feedback control law and up-date law for on-line tuning of the weighting factors of the direct adaptive fuzzy-neural controller are de-rived. By using the strictly-positive-real (SPR) Lyapunov theory, the stability of the closed-loop sys-tem can be guaranteed. Simulation results demon-strate the effectiveness of the proposed control scheme for ABS control.