Recent theorists argue that gratitude, besides encouraging social exchange, serves an important function of relationship building. However, there is a lack of research exploring the specific behaviors through which gratitude promotes relationship building. Given that behavioral mimicry serves important affiliative needs, we explored whether gratitude promotes behavioral mimicry. We found that participants who received intentional help later mimicked the behavioral mannerisms of their benefactor. This mimicry tendency was not extended to a nonbenefactor. In contrast, participants who ended up with the same positive outcome, but believed that it was attributable to chance, did not exhibit a reliable level of mimicry. Our results suggest that nonconscious behavioral mimicry might be a subtle but important first step through which gratitude promotes communal relationships.