The rapid spread of social media has brought new ways for marketers to communicate and manage brands online. Celebrity endorsement has been a popular practice in social media, however, what contributes to its effectiveness has not been fully understood. To address this issue, this study examines the effects of endorsement in social media towards brand attitude and merchandise attractiveness based on the source credibility model. We propose source credibility elements: attractiveness, expertise, and trustworthiness, to be positively related to consumer attitude. We test these hypotheses by conducting online survey with 183 participants in Indonesia. This study demonstrated that brand attitude was influenced by endorser’s attractiveness and trustworthiness, meanwhile merchandise attractiveness was influenced by endorser’s expertise and trustworthiness.