As we detect defects and eliminate them in early stages, we can make better quality software. For doing this task, we need to use a defect tracking system which con effectively track and manage defects that give severe effects on software quality. Those existing defect tracking systems have some weaknesses as we apply them to organizations that use CMMI for process improvements. Major problems of those systems are that they require the organizations to collect many types of defect data at a time without providing the proper explanation and even without the support of defect management process. The organizations at CMMI maturity level 2 and 3 have problems for analyzing those defects because there is no specific process area at CMMI maturity level 2 and 3 which directly handles defect managing activites. This paper resolves those problems by developing a defect tracking system which offers methods of managing defects. And the system provides guidelines of which defects should be gathered for each CMMI mathurity levels. The system also has functions to generate various status and statistic information on defects, and to assign defect data to the person in charge so that he or she track the defect to the closure