The percent of families with parents from different racial or ethnic backgrounds has risen exponentially in the last decades. Approximately 14% of children were born into multiethnoracial (MER) families in the United States in 2015, more than double the rate from 1980 (Bialik, 2017). Studies show that MER couples are more likely to separate or divorce than their monoethnoracial (MoER) counterparts, perhaps due to greater conflict stemming from differing values, coping strategies, and conflict management styles and decreased access to family and community support (Fu, Tora, & Kendall, 2001; Zhang & Van Hook, 2009). With the growing rates of MER couples, there has been increased interest and research addressing the unique benefits and challenges of being in a MER relationship. It is likely that the challenges that arise in MER families peak across the transition to parenthood when couples must negotiate how to merge their respective values, behaviors, and beliefs into a new family unit. The proposed study examines how the ethnoracial composition of couples (i.e., same versus different racial/ethnic backgrounds) predicts levels and increases in coparental conflict across early parenthood; and, in addition, the role of familial support as both a mediator and moderator of this relationship. Identifying the processes linking couples’ ethnoracial composition to the quality of family relationships could help inform parent interventions to better support MER parents across the transition to parenthood.