In this paper, an active fault tolerant attitude control approach is provided for a flexible spacecraft to accommodate the unknown sensor faults.Firstly, a model-based fault detection and estimation technique is developed into the process behavior by using a virtual filter and an adaptive observer.Secondly, a reconfigurable attitude controller design is developed by combining both adaptive integral sliding mode control and linear matrix inequality technique.Finally, the effectiveness of the proposed fault tolerant scheme has been verified by simulation result on a flexible spacecraft attitude control system with a time varying sensor fault.