BACKGROUND: Frail older adults constitute a significant vulnerable group with complex healthcare needs requiring collaboration between various care providers and professions. Despite this requirement, there are considerable knowledge gaps in how to achieve effective collaboration. Preventive measures such as addressing pressure ulcers, falls, malnutrition and poor oral health often receive low priority compared with treating diseases or injuries. This study aims to enhance our understanding of how care collaboration in the preventive care process (PcP) using the Senior alert (SA) register could improve patient safety and equality of care for frail older adults in Sweden. METHODS: This study, conducted over 4 years, employs an explanatory mixed methods design, divided into three phases. The study protocol comprises the two first phases. PHASE 1 QUANTITATIVE: Data from SA (2019-2021) will be analysed to compare municipalities regarding the quality of registration in the PcP. Municipalities with high and low compliance indices will be identified and analysed together with data on demographics, socioeconomics and organisation from Statistics Sweden. PHASE 2 QUALITATIVE: Focus group interviews will be conducted in residential care units in the municipalities identified in phase 1 with interprofessional teams and older persons/next of kin. Additionally, 30 semi-structured individual interviews with residential care managers and other relevant stakeholders will explore obstacles and opportunities for effective care collaboration. DISCUSSION: We foresee that the results will contribute to the development of a model for effective PcP and care collaboration that can be used to improve patient safety and quality of care for frail older adults. This model can be tested and upscaled to achieve a more effective and equitable healthcare system. ETHICS AND DISSEMINATION: The study has been approved by the Swedish ethical review authority. Dissemination plans involve publications, data deposition and engagement with healthcare stakeholders to ensure the practical application of the findings.