This study is a case study for Business Process Reengineering in hospital. We modeled at medical work process for
improvement. We cited two cases. One of them is when hospital is rebuilding. Another one is when introduction of　electronic medical recording system in hospital. In past　research，has been used the flow chart for modeling. However，flowchart is not able to express detailed work process. Therefore we used activity diagram of UML. As a resuit,we were able to express of when，who，where，what work. Thus activity diagram is useful that to modeling medical work process. In addition，BPR will lead to health care services to improve.