Providing non-trivial QoS is one of the primary goals of the grid computing. Since extensive efforts have been made on the development of basic grid components such as execution framework and resource brokering system, there is still a great challenge to build up a QoS-enabled grid architecture for today’s service grid. In this paper, a QoS-enabled service grid architecture (QESA) is proposed; the concept of differential guaranteed service is introduced to provide QoS guarantee at service layer; a QoS-aware service discovery and scheduling mechanism are designed to provide QoS guarantee for grid jobs. The performance of the QESA and related mechanisms has been evaluated by a grid application called AREM. The results show that QESA can provide QoS guarantee to grid jobs.