As e-commerce has rapidly grown in past decades, the fashion industry in Malaysia has experienced positive growth in economic values. As millennials are the biggest spenders in Malaysia, their loyalty is often left behind. In fact, millennials' brand loyalty is difficult to attain by e-commerce sellers because of their preferences in buying online products and their tendency to be cautious of marketing techniques to avoid being manipulated. Despite immense spending power, millennials were found to be very disloyal to brands. This study aims at examining various literature on brand loyalty. There are three theories integrated into this study which consist Technology Acceptance Modal (TAM), Expectation Disconfirmation Theory (EDT), and Theory of Reasoned Action (TRA). It also aspired to identify the relative importance of income as a moderator to trust as one of the most critical factors influencing millennials' brand loyalty to online fashion brands' e-commerce sites. In addition, this paper seeks to determine the moderating effect of income on the relationship between trust and millennials' brand loyalty. Based on empirical studies in marketing literature done by previous researchers, this study came out with a conceptual framework pertaining to the relationship between website efficiency, customer service, trust, and brand image on millennials' brand loyalty ware explored empirically. The study involved three hundred and ten millennial respondents, and the data collected was analyzed using Statistical Package for Social Sciences (SPSS) version 25 and the Smart-PLS version 3 software. The findings in this study illustrate that customer service, trust, and brand image significantly impact brand loyalty, and income moderates trust and brand loyalty. In conclusion, besides contributing to enriching the literature, the study can assist policymakers in developing and formulating strategies to understand online customers, particularly millennials in Malaysia.