Introduction: Breakthrough pain is common in children and adults with cancer and other conditions, including those approaching end-of-life, although it is often poorly managed, possibly partly due to a lack of validated assessment tools. This review aims to (1) identify all available instruments measuring breakthrough pain in infants, children, adolescents or adults and (2) critically appraise, compare and summarise the quality of the psychometric properties of the identified instruments using COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) criteria. Methods and analysis: Two searches will be carried out between October 2019 and January 2020, one for each aim of the review. The Cochrane Library, International Prospective Register of Systematic Reviews, Embase, Cumulative Index of Nursing and Allied Health Literature, Medical Literature Analysis and Retrieval System Online (MEDLINE), PsycINFO, Web of Science Core Collection, Google Scholar, the ProQuest Dissertations & Theses Database, Evidence Search and OpenGrey databases will be searched from database inception until the date the search is conducted. Reference lists of eligible articles will be screened and authors in the field contacted. For search 1, articles will be screened by two reviewers by abstract, and full-text where necessary, to identify if a breakthrough pain assessment was used. Search 2 will then be conducted to identify studies evaluating measurement properties of these assessments. Two reviewers will screen articles from search 2 by title and abstract. All potentially relevant studies will be screened by full text by both reviewers. For search 2, data will be extracted in parallel with the quality assessment process, as recommended by COSMIN. Two reviewers will assess methodological quality using the COSMIN Risk of Bias checklist and the COSMIN updated criteria for good measurement properties. Findings will be summarised and, if possible, data will be pooled using meta-analysis. The quality of the evidence will be graded and summarised using the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) guidelines. Ethics and dissemination: Results of this review will be submitted for publication in a peer review journal and presented at conferences. PROSPERO registration number: CRD42019155583.