Quadrotor is the one of the most popular rotary wing aircraft in control problems. There may be some problems in this system. In this case, quadrotor will not fly and do its duty effectively. In this study, a fault tolerant control strategy for a quadrotor is proposed in the presence of actuator faults. A linear mathematical model which is derived from a nonlinear model. The observer based state estimation approach is widely used in fault tolerant area. Here, this approach is used to detect and isolate faults in a quadrotor system. Generalized Observer Scheme (GOS) based Unknown Input Ob-server (UIO) is used for the isolation. Simulation results are presented to demonstrate the performance of the proposed fault tolerant control strategy.