Fitness influencers are individuals with a high presence on social media networks who can impact public opinion with posts about activities in the gym and consumption of sport supplements. Companies recognize the importance of fitness influencers and engage them as brand representatives by closing various forms of collaboration so influencers can promote sports supplements through social networks. Influencers have the ability to influence opinions and behavior of their followers and also purchase intention for the products they promote through social networks. If the influencer is perceived as credible, he has greater power to influence the purchase intention of his followers. The credibility of influencers has three dimensions: trustworthiness, attractiveness and expertise. If influencer has all three dimensions of credibility, it is considered that he has greater power to impact the followers` purchase intention. The aim of the research is to determine whether the aforementioned dimensions of fitness influencers` credibility affects the followers intention to purchase sports supplements promoted by influencers through social networks. In order to fulfill the aim, a research was conducted in which participated 100 respondents who follow at least one fitness influencer on social networks. Data were collected through a structured questionnaire created in Google Forms. The research established how respondents consider fitness influencers as credible and how they believe that fitness influencers have all three dimensions of credibility: trustworthiness, expertise and attractiveness. However, no relationship was established between the credibility of fitness influencers and purchase intention of sport supplements among their followers.