Health literacy refers to an individual's ability to engage with health information and services. Cancer caregivers play a vital role in the care of people with cancer, and their capacity to find, understand, appraise and use health information and services influences how effectively they are able to undertake this role. The aim of this study was to develop an instrument to measure health literacy of cancer caregivers.Content areas for the new instrument were identified from a conceptual model of cancer caregiver health literacy. Item content was guided by statements provided by key stakeholders during consultation activities and selected to be representative across the range of cancer caregiver experiences. Content validity of items was assessed through expert review (n = 7) and cognitive interviews with caregivers (n = 16).An initial pool of 82 items was generated across 10 domains. Two categories of response options were developed for these items: agreement with statements, and difficulty undertaking presented tasks. Expert review revealed that the majority of items were relevant and clear (Content Validity Index > 0.78). Cognitive interviews with caregivers suggested that all except three items were well understood.A resultant 88 item questionnaire was developed to assess cancer caregiver health literacy. Further work is required to assess the construct validity and reliability of the new measure, and to remove poorly performing and redundant items, which will result in a shorter, final measure. The new measure has the potential to inform the development and evaluation of interventions and the improvement of health service delivery to cancer caregivers.