<p>Sleep disturbances are common among patients with breast cancer and may substantially impair quality of life, emotional well-being, and treatment experiences. However, evidence from Palestine and similar low- and middle-income settings remains scarce. This study aimed to assess the prevalence of poor sleep quality among Palestinian women with breast cancer and to identify factors associated with it. A multicenter cross-sectional study was conducted between December 2025 and February 2026 in three major oncology referral hospitals in the West Bank, Palestine. A total of 212 adult women with histopathologically confirmed breast cancer were recruited using convenience sampling. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI), insomnia severity using the Insomnia Severity Index (ISI), and daytime sleepiness using the Epworth Sleepiness Scale (ESS). Quality of life was evaluated using the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire-Core 30 (EORTC QLQ-C30) and breast cancer-specific module (QLQ-BR23). Multivariable binary logistic regression was performed to identify independent factors associated with poor sleep quality. Poor sleep quality was highly prevalent, affecting 78.8% of participants. In addition, 39.6% had moderate-to-severe insomnia and 47.6% reported excessive daytime sleepiness. Participants showed moderate impairment in several quality-of-life domains, particularly role and emotional functioning, alongside high symptom burden, especially fatigue and pain. Poor sleep quality was significantly associated with cancer stage in bivariate analysis (<i>p</i> = 0.041), with stage IV disease observed only among poor sleepers in the available data; however, this association did not remain significant after adjustment. Higher PSQI scores were strongly correlated with insomnia severity (<i>r</i> = 0.829, <i>p</i> &lt; 0.001) and moderately correlated with daytime sleepiness (<i>r</i> = 0.308, <i>p</i> &lt; 0.001). Poorer sleep quality was also significantly associated with lower global health status/QoL, physical functioning, and emotional functioning, and with higher fatigue, pain, and insomnia symptom scores (all <i>p</i> &lt; 0.001). In adjusted analysis, excessive daytime sleepiness was the only independent factor associated with poor sleep quality, with participants reporting excessive daytime sleepiness having markedly higher odds of poor sleep quality compared with those with normal daytime sleepiness (adjusted OR = 10.99, 95% CI: 3.92–30.30, <i>p</i> &lt; 0.001). Poor sleep quality is highly prevalent among breast cancer patients in Palestine and is closely associated with excessive daytime sleepiness and impaired quality of life. Although cancer stage showed a bivariate association with sleep quality, excessive daytime sleepiness was the only independent factor associated with poor sleep quality after adjustment. Routine sleep screening and supportive sleep-focused interventions should be integrated into oncology care to improve patient well-being.</p>