We examined how witnessing fat talk on Facebook influenced the body satisfaction and psychological well-being of Korean and U.S. young women. Korean (n = 137) and U.S. (n = 159) women completed an online questionnaire after viewing a randomly assigned mock-up Facebook page where body size of the profile owner and the messages from her peers were manipulated. Findings showed that (a) Koreans witnessing an underweight peer's fat talk reported lower body satisfaction than did those witnessing an overweight peer's fat talk, but the peer's body size did not affect the U.S. women, and (b) Koreans witnessing messages discouraging weight loss reported greater psychological well-being than did those witnessing messages promoting weight loss, whereas peers' comments did not influence the U.S. women.