This paper presents an observer-based adaptive control for uncertain nonlinear systems with input saturation and output constraints. Backstepping technology is used in the controller design. A state observer is established to estimate the unmeasured states. An asymmetric barrier Lyapunov function (BLF) with prescribed performance is constructed to deal with the output constrains. The input saturation is solved by using Nussbaum function-based method. The dynamic surface control (DSC) technique is employed to reduce the complexity of the virtual control. It is illustrated that all the closed-loop signals are semi-global uniformly ultimately bounded (SGUUB). Finally, a simulation example verifies the proposed results.