Service-Oriented Architecture (SOA) is widely adopted for building mission-critical systems, ranging from on-line stores to complex airline management systems. How to build reliable SOA systems becomes a big challenge due to the compositional nature of Web services. This paper proposes an adaptive QoS-aware fault tolerance strategy for Web services. Based on a user-collaborated QoS-aware middleware, SOA systems can dynamically adjust their optimal fault tolerance configurations to achieve optimal service reliability as well as good overall performance. Both the subjective user requirements and the objective system performance of the Web services are considered in our adaptive fault tolerance strategy. Experiments are conducted to illustrate the advantages of the proposed adaptive fault tolerance strategy. Performance and effectiveness comparisons of the proposed adaptive fault tolerance strategy and various traditional fault tolerance strategies are also provided. Keywords Web service