The literature on influencer marketing has identified opinion leadership of influencers and parasocial relationship with influencers as two focal constructs affecting followers' purchase intention; yet they are only studied in isolation. This research aims to provide a comprehensive understanding of the effects of the two key constructs by combining and comparing them in a model with the moderators of post characteristics, namely post type and correspondent inference. Empirical results from 409 online followers of two Instagram accounts confirm the complementary effects of opinion leadership and parasocial relationship in influencer marketing and reveal the more prominent role of parasocial relationship over opinion leadership in affecting followers’ purchase intention. These effects are moderated by post characteristics. Storytelling posts intensify both effects. Correspondent inference enhances the effect of parasocial relationship, but not that of opinion leadership. These findings point to the importance of the social aspect of influencer marketing and inform the influencer marketing research and practice on “who says what” for improving communication effectiveness.