Many organizations have begun to consider implementing applications using reusable components. They envision that writing a component once and reusing it in many subsequent software systems will effectively amortize the development cost among all users. Recent technology advances such as JavaBeans/EJB, COM, CORBA, and others spur this interest. However, systematic development process and practical instructions for building software components have not been studied enough. In this paper, we propose a practical object-oriented component development methodology(COMO) that can be utilized in developing software components. COMO extends Unified Modeling Language(UML) and Rational's Unified process with semantics related to component development. Since COMO provides systematic process and comprehend instruction for each development task, we believe it can be effectively used in modeling and implementing software components.