Previous research have mainly conducted research to determine how consumers as individuals are influenced by word-of-mouth. However, consumers do not exist only as individuals; they are also members of a group and are influenced by word-of-mouth. This study named the word-of-mouth influence that occurs when consumers perceive themselves as belonging to a group as the intergroup word-of-mouth effect, and explored how it differs from the word-of-mouth effect revealed in existing studies. To explain the effect of intergroup word-of-mouth, this study applied social identity theory, which has been studied in the field of psychology, to understand how the influence of positive and negative word-of-mouth can vary. To verify the established hypotheses, this study conducted experimental studies. As a result of the studies, it was confirmed that compared to general word-of-mouth, the influence of negative intergroup word-of-mouth decreases and the influence of positive word-of-mouth increases. Additionally, it was confirmed that the intergroup word-of-mouth effect can vary depending on the level of identity fusion. Specifically, in groups with a high level of identity fusion, the influence of positive intergroup word-of-mouth increased, and conversely, the influence of negative intergroup word-of-mouth decreased further. Finally, based on the research results, the academic and practical implications were proposed.