Purpose <p>To elucidate the accurate roles of dysfunctional sleep beliefs in modulating cancer-related fatigue (CRF), identify distinct sleep hygiene profiles, and assess whether and how these profiles serve as mediators in lung cancer patients undergoing chemotherapy.</p> Methods <p>This study recruited 396 lung cancer patients receiving chemotherapy between May and December 2023. Participants completed the Sleep Hygiene Index, Brief Fatigue Inventory, and Dysfunctional Beliefs and Attitudes about Sleep Scale. Latent profile analysis (LPA) was conducted to identify profiles of sleep hygiene, and mediation analysis was performed to explore the impacts of sleep hygiene profiles and dysfunctional sleep beliefs on CRF.</p> Results <p>LPA revealed three distinct sleep hygiene profiles: normal (33.3%), excellent (50.3%), and poor (16.4%). Family monthly disposable income, radiotherapy, and performance status were identified as influential factors distinguishing these profiles. Additionally, the dimensions of dysfunctional sleep beliefs and sleep hygiene profiles showed different correlations with CRF. With the normal sleep hygiene group as reference, mediation analysis revealed that poor sleep hygiene serves as a mediator between sleep worry of dysfunctional sleep beliefs and CRF (SE = 0.010, 95% CI [0.006, 0.047]).</p> Conclusions <p>This study contributes to understanding the heterogeneity in sleep hygiene in lung cancer patients undergoing chemotherapy and elucidates the underlying mechanisms of the relationship between sleep worry of dysfunctional cognitions and CRF. Clinical healthcare providers developing targeted interventions in terms of sleep beliefs and sleep hygiene might be helpful to alleviate CRF in this population.</p>