Purpose <p>This study aimed to examine the sequential mediating roles of nutritional status and depressive symptoms in the relationship between frailty and cognitive function in breast cancer patients.</p> Methods <p>A cross-sectional study was conducted with 425 middle-aged and older breast cancer patients. Frailty was assessed using the FRAIL Scale. Nutritional status was measured with the Mini&#xa0;Nutritional Assessment-Short Form. Depressive symptoms were evaluated using the depression subscale of the Hospital Anxiety and Depression Scale. Cognitive function was assessed with the Mini-Mental State Examination. Data were analyzed using the PROCESS macro for SPSS to test a sequential mediation model.</p> Results <p>Frailty was significantly associated with poorer cognitive function. A significant sequential indirect pathway was identified in which frailty was significantly associated with poorer nutritional status, and poorer nutritional status was significantly associated with more severe depressive symptoms, which were further associated with lower cognitive scores. The standardized indirect effect was <i>β </i>= -0.437, 95% CI [− 0.669, − 0.218], accounting for 43.4% of the total effect. A direct effect of frailty on cognition remained.</p> Conclusions <p>The association between frailty and cognitive function in breast cancer patients was partly explained by nutritional status and depressive symptoms within the sequential mediation model, highlighting the connection between physical and mental health.</p> Implications for Cancer Survivors <p>For breast cancer survivors with frailty, integrated care that addresses both nutritional deficits and depressive symptoms may be key to reducing cognitive decline and maintaining quality of life.</p>