IJNMRM is an online (e-journal) Malnutrition in institutionalized older people is a serious problem that has negative impact on patient outcomes. Recent literature reports that prevalence of malnutrition in hospital settings ranges from 30% to 50%. Health professionals give less priority to nutritional care in institutionalised older people than other health care interventions. Therefore, there is a general negative attitude toward this issue in health professionals. To describe the process of development of a complex intervention (CI) based on the Medical Research Council (MRC) framework, to fight malnutrition in older people in hospital settings. We have identified the theory of planned behaviour (TPB) and implementation science as the conceptual framework on which to develop the complex intervention. Our target populations are nurses that work in geriatric wards and inpatients over 65 residing in those wards. Based on literature and our preliminary studies we have identified three ingredients of the complex interventions: (1) to involve local political and hospital management; (2) interactive workshops on best nutritional care with nurses of the wards involved in the study; (3) change in the routine of nutritional care during mealtimes and introduction of a validated tool to assess nutritional status. We would expect to improve nurses’ attitudes toward nutritional care and reduce malnutrition. This article describes the development phase of a CI based on the MRC framework to fight malnutrition in older people in hospital settings. The development of a CI to fight malnutrition in hospital settings is a novel strategy that, based on our knowledge, has never been reported in literature. It could be a more effective strategy to fight malnutrition because it tries to change the attitudes of nurses’ and all other actors involved in this issue and underline each individual’s responsibility.