The COVID-19 pandemic has underscored the importance of understanding how social norms influence preventative health behaviors across cultures. Based on the theory of normative social behavior (TNSB), this study investigates the direct and moderated effects of social norms on intentions to wear masks and practice social distancing cross-culturally during the peak of COVID-19 in 2020. Representative samples were recruited from the United States (N = 333) and Italy (N = 331), two countries with different cultural tightness-looseness and orientations (individualistic-collectivistic; indulgence-restraint; uncertainty avoidance). Results revealed that perceived descriptive norms directly influenced behavioral intentions in the U.S., while perceived injunctive norms were more influential in Italy. Outcome expectations moderated the relationship between descriptive norms and mask-wearing intentions in both countries. Specifically, as perceived benefits increased, the effect of norms on mask-wearing intentions attenuated in both countries. Group identity strengthened the association between descriptive norms and mask-wearing intentions only in Italy. These findings highlight that cultural differences play an important role in normative influence mechanisms, with the U.S. being more influenced by what others do (descriptive norms) and Italy by what others approve of (injunctive norms). The study contributes to the refinement of the TNSB and emphasizes the importance of considering cultural factors in developing effective norm-based interventions to address global health challenges.