BackgroundPerceived cognitive impairment is a significant symptom experienced by breast cancer patients and may be affected by sleep quality. Coping styles have potential relevancies with both sleep quality and perceived cognitive impairment. However, the empirical evidence supporting their association among breast cancer patients is limited. ObjectiveThis study explored the associations between sleep quality, coping styles, and perceived cognitive impairment and tested the mediating role of coping styles in breast cancer patients. MethodsA total of 294 breast cancer patients were included in this cross-sectional study. Patients were assessed using the Pittsburgh Sleep Index Scale, the Simplified Coping Styles Questionnaire, and the Functional Assessment of Cancer Therapy-Cognitive Functioning (Version 3) Scale. The data were analyzed using SPSS and Process macros. ResultsThe direct effect of sleep quality on reported cognitive impairment was significant (beta = -0.245, P < .001). Furthermore, sleep quality was found to have a significant indirect effect on perceived cognitive impairment through positive coping style (beta = -0.026, P < .05) and negative coping style (beta = -0.131, P < .05). ConclusionsOur research suggests that sleep quality has both a direct effect on perceived cognitive impairment and an indirect effect through positive and negative coping styles in breast cancer patients. Moreover, negative coping style had a more pronounced mediating effect than positive coping style. Implications for PracticeClinical medical staff could reduce the perceived cognitive impairment of breast cancer patients by improving their sleep quality and encouraging them to adopt a more positive coping style.