Aspect-Oriented Programming (AOP) has been considered ing abstraction principle to reduce the problem of code tangling and make software structure clean and configurable. This paper addresses the aspect support in the design level while it has been focused mainly in the implementation/coding phase. We propose an extension to Unified Modeling Language (UML) to support aspects properly without breaking the existing UML specification. This allows developers to recognize and understand aspects in the design phase explicitly. Also, we propose a XMLbased aspect description language, UXF/a. It provides the interchangeability of aspect model information between development tools such as CASE tools and aspect weavers.