Microblog services are such new communication channels with some considerable potential to improve information sharing. The idea of sharing short messages using multiple access points seems to be appealing to people worldwide. Through the lens of flow and social identity, we explored factors that influence information sharing behaviors in microblog services. With an empirical study, we examined enjoyment and concentration(flow) and self-presentation(social identity) in microblog services like twitter can contribute to the user behaviors. Our aim was to gain insight into ways of creating an environment that facilitating voluntary sharing of information. Our findings suggested that enjoyment, concentration, and selfpresentation were crucial determinants of information sharing behaviors in microblog services. This study has important implications for academic researchers and practitioners who seek to understand why microblog service users share their information with other members in microblog services.