Twitter, a 140-character microblogging social networking service, has garnered attention from researchers and practitioners due to its considerable potential for information diffusion. Prior studies on Twitter typically focused on how user traits or relationships in a network affect information diffusion. However, few studies have been conducted on how posted messages in the service influence this phenomenon. Thus, this paper focuses on posted messages (a.k.a. “tweets”) and how they affect individuals’ information sharing behaviors on Twitter. A model for investigating tweet sharing behavior on Twitter is proposed based on dual-process theory and on social cognitive theory. Results from a preliminary test show that individuals’ perceptions of the argument quality and source credibility of a received tweet play a major role in their information sharing behavior via the perceived level of usefulness of the information and self-efficacy in regard to the sharing of a received tweet. Additionally, the existence of external links in a tweet moderates the impact of argument quality on users’ attitudes toward received tweets.