This paper describes experience gained and lessons learned from restructuring OODesigner, a Computer Aided Software Engineering (CASE) tool for Object Modeling Technique (OMT). This tool supports a wide range of features such as constructing the three models in OMT, managing information repository, documenting class resources, automatically generating C++ and Java code, reverse engineering C++ and Java code, searching and reusing classes in thecorresponding repository and collecting metrics data. We had developed the version 1.x of OODesigner during 3 years since 1994. Although we had developed this version using OMT and C++, we recognized the potential maintenance problem that originated from the ill-designed class architecture. Thus we totally restructured that version during 12 months, and we got a new version that is much easier to maintain than the old one. In this paper, we present what we did to restructure it and what we gained after the restructuring, and we also present a brief overview of the major features of OODesigner.