Marital communication and cognitive challenges, including diminished marital intimacy and cognitive flexibility, are fundamental issues in marital relationships that can negatively affect marital stability and quality of life.Therefore, this study aimed to examine the effect of self-differentiation-based intervention on marital intimacy and cognitive flexibility in couples exhibiting emotional cutoff syndrome.This quasi-experimental study employed a pretest-posttest design with a control group. The statistical population consisted of married couples with emotional cutoff syndrome who visited Mehraein Psychological Counseling Center in Malayer, Iran, in2024.A convenience sample of40participants was selected and randomly assigned to either the experimental(n=20)or control group(n=20).Measurement tools included the Self-Differentiation Scale(Skowron & Friedlander, 1998),Marital Intimacy Needs Questionnaire(Bagarozzi, 2001),Cognitive Flexibility Inventory(Dennis & Vander Wal, 2010),and a self-differentiation intervention protocol.The experimental group underwent10sessions of90-minute self-differentiation therapy, while posttests were administered to both groups. Data were analyzed using multivariate analysis of covariance.MANCOVA results indicated a significant difference(p<0.01)in post-intervention scores of marital intimacy and cognitive flexibility between the experimental and control groups. The self-differentiation intervention significantly improved both marital intimacy and cognitive flexibility(p < 0.01).The findings confirm the efficacy of self-differentiation intervention in enhancing marital and cognitive relationships.Thus, this approach can serve as an effective strategy in family counseling centers and couple education programs.