Recently semantic web studies are running only complicated direction, so its technology does not seem to be applied at an early date. This paper suggests a simple structure of ontology and a method to utilize this ontology in contextual advertising. The present contextual advertising systems use DB systems for search-based advertising. In these systems, there is just a list of keywords, but no relation among keywords at all. This structure is not suitable to the contextual advertising which matches an advertisement, analyzing the contents. Therefore, a discord between content and matched advertisements often happens. In this paper, we propose an intelligent keyword management system, which considers a contextual situation with expanding keywords. The keywords and the relations between them are expressed as ontology. As this proposed system uses parts of the current contextual advertising system, as it stands, only slight changes in the system can make it recommend more suitable keywords for contextual advertising.