The purpose of the current study is to explicate the theoretical structure of online authenticity and to reveal the relationship between the need for popularity (NFP) and online authenticity. A survey-based research was conducted with 573 randomly selected active users of a popular microblogging service in South Korea. Drawing on a representative sample, we tested the discriminant validity of online authenticity. Exploratory factor analysis (EFA) followed by confirmatory factor analysis (CFA) validated two factors that underlie microblogging users’ online authenticity: sense of real me (SRME) and expression of real me (ERME). As hypothesized (predicted), the NFP was a significant predictor of online authenticity: Microbloggers with higher NFP had lower SRME and ERME than those with lower NFP. Age and gender were negatively correlated with both NFP and online authenticity: Younger microbloggers had higher NFP and lower SRME and ERME than older microbloggers. Male microbloggers had higher NFP and lower SRME and ERME than female microbloggers. Theoretical and practical implications for future studies are discussed.