Background <p>Cancer has become a major public health problem threatening human health worldwide. Affected by the disease and treatment, cancer patients bear heavy burdens, which shows a state of social isolation. Accurately assess the social isolation problem of cancer patients and formulate effective intervention measures, which are of great significance for promoting cancer patients’ return to families and society and improving quality of life. This protocol aims to evaluate scientifically the psychometric properties of social isolation assessment tools for cancer patients, which provides a reference for medical staff to select the most appropriate tool in clinical practice.</p> Methods <p>This protocol will follow the checklist of Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) 2015. The PRISMA-COSMIN for Outcome Measures instruments (OMIs) 2024 guideline will be applied in this study to report the psychometric properties of each assessment tool. Systematic searches will be conducted for studies related to the psychometric properties of social isolation assessment tools for cancer patients in CNKI, WANFANG, VIP, CBM, PubMed, Web of Science, CINAHL and Embase. Two graduate students who have completed the study of the COSMIN guidelines will conduct studies screening, data extraction, quality evaluation, evidence classification independently, and will give recommendations.</p> Discussion <p>Although there are many types of assessment tools for social isolation of cancer patients at present, there is a lack of systematic evaluation of their psychometric properties. The findings from this review may contribute to the optimization of assessment tools and the proposal of improvement suggestions, and provide reference for medical staff when choosing appropriate assessment tools.</p> Systematic review registration <p>PROSPERO CRD420251041263.</p>