Three studies involving a total of 844 individuals were conducted to develop and validate the Resentment Rating Scale for Couples (RRS-C), a new measure assessing resentment that may exist in a relationship. The studies examined the dimensionality, internal consistency, and construct validity of the new scale. The final instrument comprised 13 items that had adequate internal consistency. Convergent validity of the new measure was indicated by its significant relationships with the Dorman Resentment Rating Scale (DRRS), relationship variable, namely frequency of conflict, and indicators of psychological well-being, namely overall satisfaction and happiness in a relationship. The scale discriminated resentment from anger (Novaco Anger Scale), anxiety (Beck Anxiety Inventory) and jealousy (Multidimensional Jealousy Scale). Implications for future research of the present study are discussed.