UML 2.0 activity diagrams (ADs) are largely used as a modeling language for flow-oriented behaviors in software and business processes. Unfortunately, their place/transition operational semantics is unable to capture and preserve semantics of the newly defined high-level activities constructs such as Interruptible Activity Region. Particularly, basic Petri nets do not preserve the non-locality semantics and reactivity concept of ADs. This is mainly due to the absence of global synchronization mechanisms in basic Petri nets. Zero-safe nets are a high-level variant of Petri nets that ensure transitions global coordination thanks to a new kind of places, called zero places. Indeed, zero-safe nets naturally address Interruptible Activity Region that needs a special semantics, forcing the control flow by external events and defining a certain priority level of executions. Therefore, zero-safe nets are adopted in this work as semantic framework for UML 2.0 activity diagrams. Keywords: UML Activity Diagrams Formalization, Interruptible Activity Region, Zero-Safe Nets. For further information, please visit this web site.