Background: Because of the increasing 5-year survival rate of breast cancer, adjustment to breast cancer survivorship is pertinent to the patient's life after diagnosis. Despite the psychological changes occurring during the transitional period (first 5 years after diagnosis) and after primary therapy having a known, critical effect on survivorship status, the data related to this topic are very limited. Purpose: This studywas designed to examine the relationships among demoralization, stress, sleep disturbance, and psychological well-being in women with breast cancer after primary therapy. Methods: Two hundred eight women with breast cancer (mean age = 51.96 ± 8.27) participated in a cross-sectional study in central Taiwan. Recruitment was conducted using convenience snowball sampling at a local teaching hospital. All of the participants had completed primary therapy and were in the 5-year postdiagnosis period. The average duration of cancer was 28 months. The participants completed the Stress of Breast Cancer after Primary Therapy Scale, Demoralization Scale, Pittsburgh Sleep Quality Inventory, and Ryff's Psychological Well-Being Scale–Short Form. Data were analyzed using a structural equation model to find plausible path relationships among stress, demoralization, sleep disturbances, and psychological well-being. Results: Demoralization was shown to completelymediate the effect of stress on sleep disturbances. In addition, the predictive effect of sleep disturbances on psychological well-being was overwhelmingly explained by demoralization when competing with sleep disturbances. Furthermore, a positive path was found between stress and psychological well-being because of the suppression effect of demoralization. Conclusions/Implications for Practice: Demoralization was found to be a mediator that suppressed the relationships among stress, sleep disturbances, and psychological well-being in the adaptation process of patients with breast cancer after primary therapy. This article adds to the limited research on women with breast cancer after primary therapy who are in their initial 5 years of diagnosis. In addition, this study used structural equationmodel to find the plausible path relationships among the psychological factors involved in the well-being of women with breast cancer. Supporting patients with cancer and effectively reducing their perceived demoralization will be key to transforming stress into personal growth and a facilitator of long-term recovery.