As the Unified Modeling Language (UML) becomes an industrial standard for object-oriented software development, many system models have been specified in UML notation. A system can be described in terms of the functional view through the use case model, the static view through the class model, and the dynamic view through activity or sequence model. In particular, activity model has more to do with the subject of the modeling and the experience of the modeler; for business modeling, for modeling the logic captured by a single use case or for modeling the detailed logic of a business rule. In this paper we propose mapping rules and a transformation algorithm to translate a UML activity diagram into a Colored Petri Nets (CPNs).