Today, many fashion companies use brand extension and it is especially important to conduct brand extension that coincides with consumer self-image, and maintains brand loyalty in order to succeed. The purpose of this study is to investigate the effect of congruency of parent brand image with self-image, brand loyalty, and brand involvement on the attitude towards extended product in fashion brand extension. A survey questionnaire was used to collect information from 170 female college students, and collected data were subjected to descriptive analysis, factor analysis, and regression analysis. Results showed that the congruency of parent brand image with self-image had a positive effect on the attitude towards extended product in fashion brand extension, with a positive mediating effect of brand loyalty, and a negative mediating effect of brand involvement. Also, the congruency of parent brand image with self-image and brand loyalty of the parent brand had a positive effect on the attitude towards the extended product, whereas brand involvement had a negative mediating effect on the attitude towards the extended product in fashion brand extension. The results of this study provide some useful suggestions to marketers in fashion industry: marketers should consider some psychological aspects of consumers such as congruency of parent brand image with self-image, brand loyalty, and brand involvement when conducting brand extension.