Applying UML modeling to both software component testing (SCT) and software component development enables testing and design phases to utilise a consistent specification approach to producing functional and reliable software components with better effectiveness and efficiency. This paper introduces a new UML-based SCT methodology, model-based software component testing (MBSCT), which is developed with a set of SCT techniques. Following the proposed MBSCT framework for developing component test cases, the main task in the first phase is to build a set of UML-based test models, which is supported with the scenario-based component integration testing and test by contract techniques. The main task in the second phase is to design and generate component test cases from the constructed test models, which is supported with a component test mapping technique. The working process and effectiveness of the MBSCT methodology is demonstrated with a case study of a typical component-based system.