Objectives: This study sought to explore the effect of the family involvement in care (FIC) intervention on family and staff well-being over a nine-month period in a long-term care (LTC) facility providing dementia care. Method: A quasi-experimental design with randomised allocation of two LTC sites but not the participants was employed. Family caregivers (n=57) of residents with dementia and staff (n=59) from two LTC facilities in Queensland Australia, were recruited. Participants were assessed once pre-intervention and three times postintervention for knowledge, stress and satisfaction outcomes. Between-group and within-group effects were analysed using ANOVAs at 50.05 level of significance. Pre- and post-intervention interviews from a purposive sample of family caregivers were also conducted to enhance understanding of FIC benefits. Results: Beneficial intervention effects associated with family caregivers' knowledge of dementia were found ( p<0.001). Negative intervention effects were also found for family satisfaction outcomes in relation to staff consideration of their relatives and management effectiveness ( p<0.05). In addition, staff well-being and job satisfaction were found to be negatively affected by their perceived inappropriate behaviour of residents with dementia (p<0.05). Conclusion: Participation in the FIC intervention improved family caregiver knowledge. The major barrier to the success of the partnership intervention in achieving beneficial long-term psychosocial effects for family and staff caregivers was lack of resources and leadership required to support collaboration between family and staff, mainly due to environment and structural changes. This study contributes to our understanding of the importance of partnerships in promoting family involvement in dementia care.