The evolution of digital technologies are fundamentally transforming marketing and changing how communication works today. With the emergence of Internet and social media platforms, consumers can now easily access information, share recommendations on product reviews, and conduct online purchases, particularly the millennials. The shift of information sharing causes consumers to no longer perceive brands and companies' marketing messages as credible, causing brands and companies to work with influential people. Social media influencers (SMIs) are used as product endorsers to communicate brand's messages, provide recommendations on endorsed products, and generate influence on target audiences. Hence, source credibility of SMIs is important in measuring effectiveness and persuasiveness of the communicated message by SMIs that influences consumer purchase intention. The aim of this study is to find out whether social media influencers' (SMIS') source credibility that is characterized in three dimensions comprising of attractiveness, expertise, and trustworthiness have a positive and significant influence towards millennial consumers' online purchase intention. This study uses a non-probability sampling with judgement sampling method. Data collection was carried out by distributing 130 questionnaires to millennial respondents who intends to conduct online purchase based on SMIs' credibility in providing recommendations or opinions of the endorsed product. The data collected were then tested for validity and reliability, and analyzed using Partial Least Square-Structural Equation Modeling (PLS-SEM) method, which runs through SmartPLS version 3 software. The results showed that SMIs attractiveness, expertise, and trustworthiness positively and significantly influences millennial consumers' online purchase intention.