In recent years, firms are making significant investments in online influencer endorsement. The effectiveness of online influencer endorsement and ways to develop effective endorsement strategies however are not clear. In this study, we conduct an exploratory study and empirically test the impact of online influencer endorsement on product sales. Using endorsement information from microblog site, Sina Weibo and sales data from online e-commerce platforms, Taobao and Tmall, we found positive impacts of online influencer endorsements on sales and the effect of online endorsement is stronger for influencers with more followers. We also found evidence that frequently endorsing products is counterproductive to the online influencer’s endorsement effort. The results of this study contribute to celebrity endorsement literature and practice.