While previous studies have demonstrated significant associations between partners' emotion regulation and overall well-being, few studies provide knowledge on emotion regulation in clinical couples, especially across couple therapy sessions. With 168 heterosexual couples who attended at least the initial eight sessions of couple therapy, the current study was designed to examine the intra- and inter-personal effects of emotion regulation difficulties (i.e., lack of awareness, nonacceptance, limited strategies, and impulsivity) on the development of relationship quality over the course of couple therapy. The results of the current study provide a few important findings. First, gender differences exist in emotion regulation and relationship quality. Second, across couple therapy sessions, relationship quality improves and partners change at a similar rate. Third, emotion regulation difficulties have intra- and inter-personal effects on the starting scores and rates of change of relationship quality in the process of couple therapy. For clinical implications of findings, I specifically discussed that clinicians working with couples may find it beneficial to utilize couple therapy modalities with a specific emphasis on the emotion regulation process, such as Greenberg's version of emotionally focused couple therapy. The need for future studies with more diverse samples was also discussed.