A Virtual Organization (VO) in the Grid is a collection of users and distributed resources, in which resources are shared by users. VOs are dynamically created for some goals and then disappear after the goals are achieved. Conventional Grid architectures have been proposed for a single or static VO environment. In this paper, we propose a ticket-based Grid services architecture to support the dynamic VO environment. Tickets contain information and delegated rights of resource providers, VO managers, and users. By using these tickets, the proposed architecture supports various services in the dynamic VO environment, such as VO management, fine-grained authorization, resource information, and resource management.