Polyculturalism, a relatively new intergroup ideology conceptualises culture as dynamic by emphasising intergroup connections. Previous research has linked polyculturalism to less negative attitudes towards different racial and ethnic groups. However, the underpinnings of this relationship is not well understood. It was predicted that openness to experience, agreeableness, and cognitive flexibility (alternative and control) would be associated with lower racial and ethnic prejudice and that polyculturalism would mediate these relationships. Method: The sample consisted of 391 undergraduate students and community members who completed a polyculturalism measure, openness to experience and agreeableness scales of the Big Five Aspect Scale, the Cognitive Flexibility Inventory, and the Australian Racism, Acceptance, and Culture-Ethnocentrism Scale. Results: Path analysis indicated openness to experience, agreeableness, and cognitive flexibility (alternative) were each associated with less generalised racial and ethnic prejudice, and that polyculturalism mediated the relationship between openness to experience and prejudice and cognitive flexibility- alternative and prejudice. Conclusion: Polyculturalism may be an important avenue for understanding and reducing racial and ethnic prejudice in a racially and ethnically diverse Australia. Key Points What is already known about this topic: The traits of openness to experience and agreeableness, and cognitive flexibility are associated with less negative racial and ethnic attitudes. Polyculturalism is a lay diversity ideology where culture is viewed as a dynamic and evolving system that does not provide the basis for differentiating between groups. Instead of focusing on differences between cultural groups, connections between groups through interactions are emphasised. Polyculturalism is associated with less negative attitudes towards different racial and ethnic groups among other pro-diversity attitudes. What this topic adds: This study adds to the limited research into the role of lay diversity ideologies in explaining the relationship between personality and intergroup attitudes. Openness to experience, agreeableness, and cognitive flexibility (alternative) were each associated with less generalised racial and ethnic prejudice. Polyculturalism mediated the relationship between openness to experience and racial and ethnic prejudice, and the relationship between cognitive flexibility (alternative) and racial and ethnic prejudice. The Racism Acceptance and Cultural-Ethnocentrism Scale (RACES) is a psychometrically sound measure developed for the Australian context. It is a suitable tool for measuring the effectiveness of interventions for promoting more positive intergroup attitudes.