The behavior of an agent is defined through the specification of plans and actions. Agents have a set of plans that are selected to be executed according to their goals (and other mental state information). In this paper, we propose the use of UML 2.0 activity diagrams to model agent plans and actions. We consider a plan to be an activity. Both plans and activities are composed of actions and define the action execution sequence. By using some features available in the UML 2.0 activity diagrams and defining some new ones, we demonstrate how these diagrams can be applied to model agent plans and actions. Categories and Subject Descriptors D.2[Software Engineering]: Design – representation. General Terms Design, Languages Keywords Unified modeling language, multi-agent system, plans, actions