Blogs are a new type of media that have recently become popular users on the World Wide Web and have influence throughout society. The purpose of this study is to examine social motivations influencing intention of blog usage. Based on Technology Acceptance Model and Motivation Theory, This study considered perceived usefulness, perceived ease of use, reputation, reciprocity, enjoyment of helping, social identity as the determinants of influencing the intention of blog usage. The purposed model was empirically evaluated using online survey data collected from 342 user of popular blog site in Korea (NAVER Blog , cyworld mihompy, daum blog, yahoo blog etc) The results revealed that perceived usefulness, perceived ease of use, reciprocity, social identity affected directly the intention of blog usage. Also social identity has moderate effect via reciprocity and enjoyment of helping on blog usage. This study contributes to a theoretical understanding of the factors as social motivation that affect the usage of blogs. Practically this study results provide blog service providers useful strategic insights and service guideline to enhance user's intention of blogs.