This paper examines the association between the level of similarity in the “Big Five” personality traits of the partners in different-sex couples and their risk of union dissolution. Prior research has mainly focused on homogamy in socio-economic, demographic, and cultural characteristics, such as age, education, employment, and religion. The few studies on the effects of homogamy in the personalities of the partners on separation find mixed results. We extend on this by analysing the moderating effect of education. Using data from the German Socio-Economic Panel (SOEP) for the 2005–2019 period, we follow 3958 coresidential couples and observe 534 separations. Personality is measured via the “Big Five” personality traits. We estimate discrete-time event history models for union dissolution. In addition to reporting the main effects, we calculate interactions between personality and the level of education of the partners. Our results indicate that greater dissimilarity with regard to the personality trait “openness” is associated with a higher probability to separate. However, analysing interaction effects reveals that this is relevant mainly among medium educated men. Moreover, persons with high education seem to be less likely to separate if they are dissimilar from their partner in their level of “extraversion”. These findings suggest that relationship dynamics differ across educational groups.