During the past decade, the internet in general and social media in particular has become one of the most indispensable elements creating rapid strides, enabling multiple global industries to interact and abolish certain distances in the brands and in consumers relationships. The strategy is called influencer marketing where brands have been lately integrating into their businesses through endorsements from influencers who have access to a large amount of audience has made a significant impact on the consumers’ buying intention. The objective of this thesis was to study the effect that social media and influencer marketing in the fashion industry has on millennials as online consumers in Ho Chi Minh City, Viet Nam. By examining the combination of theoretical studies, and evidences to support the theoretical findings through individual interviews with seven fashion influencers used as the sources of primary data collection, the results of thesis were collected. It is demonstrated that the perceived effect of the cooperation between social media and influencers have an obvious impact on millennials’ buying behavior regarding the fashion businesses. Finally, the results and findings with conclusions are were analyzed. In addition to the outcomes, limitation and challenges of the studies were discussed.