Previous research has suggested that ethnicity and self-construals may play a role in shaping the utility and function of emotion expression. In a 10-day daily diary study, we examined the effects of positive and negative emotion expressivity on daily and trait intrapersonal and interpersonal functioning across Asian and European American college students. One hundred fifty-five Asian Americans and 74 European Americans completed questionnaires assessing daily affect and daily interactions. Results revealed no significant ethnic group differences in the tendency to express positive or negative emotions, nor in the relationship between positive emotion expressivity and intrapersonal functioning. However, ethnic group differences were apparent in the relation between negative emotion expressivity and functioning. Asian Americans high in negative emotion expressivity were more likely to report poorer daily and trait intrapersonal functioning, whereas these relationships were unrelated for European Americans. Among highly interdependent individuals, positive emotion expressivity was associated with greater daily positive mood, lower trait interpersonal problems, and lower depressive symptoms; however, this was not shown for low interdependence individuals. Our findings suggest that the valence of emotional expressions and culture needs to be considered in studying the adaptive function of emotion expression.