Health literacy is a public health issue. Unpaid caregivers of older people with low health literacy may have difficulties providing care, exerting a negative impact on the care process. The aim of the present study was to perform a systematic review of the literature on factors associated with low health literacy in unpaid caregivers of older people. Searches for relevant articles were conducted in the Cochrane Library, Embase, LILACS, PubMed and Web of Science databases. A total of 1440 articles were identified, nine of which met the eligibility criteria and were included in the systematic review, which was registered in PROSPERO (CRD42024522986). A total of 2209 unpaid caregivers participated in the studies selected for this review. Most were women (67.2%). The average frequency of inadequate health literacy was 27.1%. Sociodemographic characteristics (i.e. advanced age, low educational level, the female sex), factors related to the care process (i.e. low acculturation, low empowerment, poor ability to read medication package inserts, lower care capacity, greater disease severity, hospitalization of care recipients), cognitive factors and factors related to quality of life/well-being (i.e. less social support, poorer quality of life, greater cognitive impairment, higher levels of burden) were associated with low health literacy. In conclusion, low health literacy in unpaid caregivers of older people is associated with sociodemographic, care-related and cognitive factors as well as factors related to quality of life/well-being. Low health literacy may exert a negative impact on the health of caregivers and, consequently, the quality of care provided to older people.