Customer loyalty is a desired and essential result for companies in a business environment with a lot of competition, of which the fashion industry is no exception. For the fashion industry, the competition between businesses is increasingly fierce with the appearance of tailored fashion brands for each customer, also known as a designed fashion brand. The objective of this study is to examine the relationship between the antecedents of the relationship (reputation of designer, social media marketing) and customer relationship (trust and intimacy), and loyalty of customer for a designed fashion brand. The mixed research method is used to achieve research objectives with qualitative and quantitative research method. Qualitative data was collected through in-depth interview with 12 participants in Ho Chi Minh City, while quantitative data was collected by a survey of 799 respondents in Ho Chi Minh City and Hanoi City. The results show that the antecedents of relationship marketing positively affect on customer relationship and customer loyalty. Moreover, customer relationship has a positive impact on the customer loyalty when shopping for fashion products. From the research results, some managerial implications are also proposed for the designed fashion brands to improve the relationship marketing performance.