Objective Personality traits are characterized by both stability and change across the life span. Many of the mechanisms hypothesized to cause personality change (e.g., the timing of various social roles, physical health, and cultural values) differ considerably across culture. Moreover, personality consistency is valued highly in Western societies, but less so in non‐Western societies. Few studies have examined how personality changes differently across cultures. Method We employed a multilevel modeling approach to examine age‐related changes in Big Five personality traits in two large panel studies of Americans (n = 6,259; Mage = 46.85; 52.5% female) and Japanese (n = 1,021; Mage = 54.28; 50.9% female). Participants filled out personality measures twice, over either a 9‐year interval (for Americans) or a 4‐year period (for Japanese). Results Changes in Agreeableness and Openness to Experience did not systematically vary across cultures; changes in Extraversion, Neuroticism, and Conscientiousness did vary across cultures. Further, Japanese show significantly greater fluctuation in the level of all the traits tested over time than Americans. Conclusions The culture‐specific social, ecological, and life‐course factors that are associated with personality change are discussed.