AIM: The aim of this study was to characterise the trajectory and to identify determinants of nutritional health over time in a sample of older hospitalised patients, using the Generalized Estimating Equation. BACKGROUND: Nutritional health deteriorates and may fluctuate over time during and post-hospitalisation. To develop a target intervention it is essential that we first have a clear picture of how the nutrition changes and examine the determinants of nutritional health during and post-hospitalisation. DESIGN: A prospective cohort study was conducted on 306 older hospitalised patients aged 65 years and older. METHODS: Subjects were recruited from five surgical and medical wards at a tertiary medical center in northern Taiwan and assessed at four points in time: within 48 hours after admission, before discharge and 3-6 months post-discharge. RESULTS: Nutritional health fluctuated significantly over time. The curve dropped during hospitalisation, returned at three months and rose slightly at six months post hospitalisation. After controlling for length of stay and surgical treatment, patients showed decreased cognitive capacity, worsening oral health, increased use of medications, increased functional limitations and raised depressive symptoms, all of which affects their nutritional health over time. The extent of functional status impacting on nutrition varies at different points in time while the predictability of other determinants remained stable. CONCLUSION: The trajectory of nutritional health is a reflection of the patients' cognitive status, oral health, medication taken, functional status and depressive symptoms. The findings of our study should provide guidance in the development of intervention for the nutritional health of older patients during inpatient as well as transitional care. RELEVANCE TO CLINICAL PRACTICE: Multi-faceted packages of interventions targeting a range of determinants for managing undernutrition and subsequent decline during and post-hospitalisation need to be tested.