This research is intended to help the development of new products and marketing strategies studying consumers knowledge level and attitude towards original brand and the extension attitude related to the brand image. The detailed purposes of this study are as follow: First, it is to measure consumers` knowledge and attitude towards original brand. Second, it is to clarify the dimensions of the image about the original brand and extended brand product which is perceived by the consumer. Third, it is to meassure image consistency and product similarity between the original brand and extended product. The sample group consisted of female college students 393 in Seoul. Stratified sampling, based on major and grade of students and the structure of the college they were attending was used as sampling method. Questionnaires, which were selected from literature and proceeding researches published in Korea and abroad, were modified for this study. SAS Package was used for data analysis. The results observed in this study were as follow: 1. Consumers` knowledge level about original brand showed high among students majoring in clothing-related subjects and their general attitude proved to be positive. 2. Image factors of original brand were classified to dignity factor, personality/modernity factor, femininity factor, and ornamentation factor. Lipstick is considered to have high image consistency and product similarity. 3. Comparing the attitude before and after extension, extension to lipstick which showed high image consistency and product similarity received more positive reactions than one to bed cover sheet. 4. It was founded that although knowledge and attitude towards original brand with image consistency had no influence on the extension attitude, knowledge and attitude without image consistency influence the extension attitude.