The purpose of this study was to examine the effects of brand knowledge on evaluations of brand extensions in fashion market. Here, consumer knowledge toward the parent brand was based on the brand and on the company which introduced the brand. The brand extensions were classified into brand-name extension and corporate-name extension. For this study, questionnaires were administered to 700 single women in twenties. The questionnaires were designed to measure brand extension evaluations and brand knowledge in terms of familiarity, use experience and self-assessed knowledge, evaluations of the attributes and attitudes based on the brand and corporate. Employing a sample of 621 women, data were analyzed by t-test. Major findings of this study are summarized as follows; 1) The higher the level of brand knowledge such as brand familiarity, brand use experience and self-assessed brand knowledge was, the higher positive effects were on the evaluations of brand-name extension. Also, evaluations of brand attributes and brand attitude positively influenced the evaluations of brand-name extension. 2) The higher the level of corporate knowledge such as corporate familiarity and use experience of product manufactured by the company was, the higher positive effects were on the evaluations of corporate-name extension. Also, evaluations of corporate attributes and attitude on corporate positively influenced the evaluations of corporate-name extension. These results demonstrate that positive knowledges and affects on the parent brand are transferred to its extended product through categorization process.