This study attempts to investigate consumers’ perceptual process of influencer advertising and its impact on brand attitude formation on social media. Perceived congruence between the influencer and the product and sponsorship disclosure are manipulated as key independent variables. In so doing, this study examines whether consumers can infer two types of motives (affective vs. calculative) from different levels of perceived congruence (high vs. low) and sponsorship disclosure (present vs. absent). The impact of multiple motive inference on brand attitude is also examined in this study. The result indicates that perceived congruence of influencer and posting has a significant effect on the affective motive inference. When the posting is perceived to be relevant to and expected from the influencer, the participants infer the affective motive of the influencer. However, the participants do not infer calculative motives from the incongruent posting of the influencer. As native advertising can obfuscate the boundary between editorial and commercial contents (Conill, 2016), perceived congruence is significant to successfully cover the posting as a natural posting by influencer and induce affective motive inference. In addition, the disclosure of sponsorship did not reveal any effect on the calculative and the affective motive inferences. Even though the disclosure of sponsorship can make viewers recognize an advertising intent (Boerman, Willemsen, & Van Der Aa, 2017), the message did not induce motives inference behind it. It is significant to investigate whether there are intervening variables that moderate the linkage between sponsorship disclosure and motive inference processing. Furthermore, affective motive inference impacted the attitude for the brand whereas calculative motive inference exerted no significant effect. These findings suggest that when the product promoted in influencer advertising is congruent with the influencer, consumers form positive attitude toward the brand through affective inference processing. To successfully implement influencer advertising, marketers should design a content congruent with the influencer’s original postings and encourage audience to engage in affective motive processing.