Recently, impressions of web pages formed by visitors have become an important tool to increase the number of repeat visitors to the web page. Therefore, the management of knowledge on consumers' impressions obtained in several study fields is an essential task in current industrial design. However, no methods that realize such knowledge management have been established. Thus, our study proposes and implements a knowledge management method that can effectively provide knowledge of impressions to web designers to help them in building attractive websites. We introduce a framework for the description of impressions that depend on perceptual fluency, which can serve as an useful indicator of pleasure. We can extract the features of objects that affect impressions on the basis of perceptual fluency. We specify the relationship between objects and impressions by modeling the concepts of awareness, perception, and self-report on the basis of an ontology development environment Hozo and a top-level ontology YAMATO. We then instantiate a case where a person has a good impression of a Web page, and we describe the relationship between a perception and a stimulus in such a case. Our approach demonstrates that ontological modeling of impressions helps us to understand the correspondences between affections and physical irritations.