Summary form only given. Workflow management systems (WfMSs) are usually designed to run with the workflow (process) definitions and artifact definitions from repository. The static characteristics for process definitions might reduce the practicability of the systems. The cost to develop a WfMS is so high that it is reasonable to take the flexibility of system architecture into account. In this paper, we present an approach to adapt to dynamic changes on workflow definitions with agents. In our agent-based workflow system, the definition of a workflow can be modified by the agent itself. Therefore, agents can modify their guidance for workers, and the system is more flexible to meet the specification modification.