A database is a collection of related data that represents some relevant reality. The database design process consists of four steps: Requirements Collection and Analysis, Conceptual Database Design, Logical Database Design, and Physical Database Design.Recently, knowledge-based computer-aided design tools have been introduced. A list of them can be found in Lo (1994). None is empowered with machine learning to improve its permanent knowledge base or inference abilities. This research applies case-based reasoning to Conceptual Database Design. Section 2 reviews related theories. Section 3 discusses design and implementation of the application. Lastly, section 4 is the conclusion.