People tend to make self-aggrandizing social comparisons on traits that are important to the self. However, existing research on the better-than-average effect (BTAE) and trait importance does not distinguish between personal trait importance (participants’ ratings of the importance of certain traits to themselves) and cultural trait importance (participants’ perceptions of the importance of the traits to the cultural group to which they belong). We demonstrated the utility of this distinction by examining the joint effects of personal importance and cultural importance on the BTAE among Hong Kong Chinese and American participants. Results showed that the BTAE was more pronounced for personally important traits among both Chinese and American participants. More important, the magnitude of the BTAE was smaller on culturally important traits among Chinese participants only. Chinese participants displayed the strongest BTAE on personally important and culturally unimportant traits, and the smallest BTAE on personally unimportant and culturally important ones. American participants showed the smallest BTAE on personally and culturally unimportant traits. These findings underscore the importance of distinguishing personal trait importance and cultural trait importance in understanding the cultural effects on self-aggrandizing social comparisons. They further suggest that in cultures where people are expected to be modest in self-expression (e.g., Chinese culture), people would avoid claiming superiority on highly culturally important traits even when these traits are important to the self.