This research was conducted to examine the hypothesis that expressing gratitude to a relationship partner enhances one's perception of the relationship's communal strength. In Study 1 (N = 137), a cross-sectional survey, expressing gratitude to a relationship partner was positively associated with the expresser's perception of the communal strength of the relationship. In Study 2 (N = 218), expressing gratitude predicted increases in the expresser's perceptions of the communal strength of the relationship across time. In Study 3 (N = 75), participants were randomly assigned to an experimental condition, in which they expressed gratitude to a friend, or to one of three control conditions, in which they thought grateful thoughts about a friend, thought about daily activities, or had positive interactions with a friend. At the end of the study, perceived communal strength was higher among participants in the expression-of-gratitude condition than among those in all three control conditions. We discuss the theoretical and applied implications of these findings and suggest directions for future research.