This study investigates cultural and communication medium effects on conversational argumentation in a decision-making context. Chinese and U.S. participants worked in pairs on two decision-making tasks via face-to-face (FtF) and instant messaging (IM). The analyses showed that Chinese participants tended to engage in potentially more complex argumentation, whereas U.S. participants tended to utilize proportionally more statements of claims and statements of convergence (agreements, acknowledgments, and concessions). Argumentation in IM tended to be more direct than in FtF interactions. There were no interaction effects between culture and communication medium on argumentation behavior. In addition, statements of convergence were found to be negatively related to measures of persuasion, indicating that such statements do not necessarily indicate true agreements or shifts in opinion. The results are discussed in terms of structuration theory and the socioegocentric model of communication. (Contains 3 footnotes and 3 tables.)