Medical crowdfunding in social media is growing to be a convenient, accessible, and secure manner to cover medical expenses. It differs from traditional donation initiatives and medical crowdfunding on non-social media platforms in that projects are disseminated via social media network and among acquaintances. Through semi-structured in-depth interviews on donation behaviors of 52 respondents, this study uses grounded theory to extract seven main categories that affect medical crowdfunding donation behavior in social media, namely interpersonal relationship, reciprocity of helping, attitude toward donation, perceived behavior control, perceived trust, project information, and characteristics of patients. In the spirit of Elaboration Likelihood Model, we develop a theoretical framework that the seven factors influence donation behavior in medical crowdfunding in social media via a central and a peripheral route.