In this paper, a new performance index is proposed for switched systems. The new performance index can be viewed as the mixed weighted H ∞ and passivity performance. This new performance index covers the weighted H ∞ performance and the passivity performance as special cases. Based on this new performance index, the weighted H ∞ filtering problem and the passive filtering problem of linear switched systems with unstable subsystems are solved in a unified framework. The states of the filtering error system constructed by the augmentation technique will be divergent when unstable subsystems are activated. To overcome this problem, a set of mode-dependent filters of a Luenberger-like observer type is constructed. The multiple Lyapunov function approach and the average dwell-time technique are employed to solve the mixed filtering problem.New sufficient conditions for the existence of mixed H ∞ and passive filters are developed, which ensure the filtering error system to be asymptotically stable with a prescribed mixed H ∞ and passivity performance index. Moreover, the desired mixed H ∞ and passive filters can be constructed by solving a set of linear matrix inequalities. Finally, numerical examples are given to demonstrate the applicability and advantage of the obtained results. KEYWORDS average dwell time, H ∞ filtering, linear switched systems, passive filtering, unstable subsystemsRecently, the research on switched systems has been developed because of many physical or man-made systems possessing switching features. 1,2 In general, a switched system is composed of a finite number of continuous-time or discrete-time subsystems and a switching signal. The switching signal, which orchestrates the switching among these subsystems, 316