Software quality is classified by quality of process and product. In experience of Quality Management, it is known that quality level of product as it depends on goodness and badness of process and organization. As a result, improvement of software process has been important subject. According as this trends, ISO 12207 is publicated as standard of software life cycle process by ISO. For UML based object oriented development process, it is necessary that we should research detailed definition of activity and task of ISO 12207 process which is added, deleted or tailored in according to organization and project characteristics. In this thesis, by according with ISO 12207 software life cycle process, UML based object oriented development process is proposed. This process is composed of 7 steps and 19 activities including development phase, activity and product to improve quality of reliability. Usefulness of object oriented process for improvement of software quality is proved at three ways, which are comparative analysis of process characteristics, SPICE process evaluation and SPICE rick analysis.