Model Driven Engineering (MDE) provides available tools, concepts and languages to create and transform models. One of the most important successes of MDE is model transformation; it permits transforming models used by one community to equivalent models used by another one. Moreover, each community of developers has its own tools for verification, testing and test case generation. Hence, a developer of one community who moves to work with another community needs a transformation process from the second community to (his/her) own community and vice versa. Therefore, the target community can benefit from the expertise of the source one and the developers do not begin from zero.In this context, we propose in this paper an automatic transformation to create a bridge between the BPMN and UML communities. We propose an approach and a visual tool for the automatic transformation of BPMN models to UML Activity Diagrams (UML-AD). The proposed approach is based on Meta-Modeling and Graph Transformation, and uses the AToM3 tool. Indeed, we were inspired by the OMG meta-models of BPMN and UML-AD and implemented versions of both meta-models using AToM3. This last allows generating automatically a visual modeling tool for each proposed meta-model. Based on these two meta-models, we propose a graph grammar composed of sixty rules that perform the transformation process. The proposed approach is illustrated through three case studies.