The ubiquity of international and intercultural collaboration over computer-mediated communication (CMC) raises questions about how culture, group cultural composition and medium influence communication. We conducted a laboratory study investigating the influences of individual cultural background (American versus Chinese), group cultural composition (same- versus mixed-culture groups), and communication medium (text-only versus video-enabled chatrooms) on the process of group brainstorming conversations. The paper presents an analysis of cultural adaptation focusing on whether and how individuals adapt their conversational behaviors when encountering group members from another culture. Chinese participants increased their responsiveness when working with American partners (i.e., mixed-culture groups). We also examine patterns of cultural adaptation by time and communication medium to gain insights for future research.