The study aims to compare the efficacy of a home-based structured exercise programme (12-step sitting Tai Chi) involving both persons with dementia and their caregivers with a standard non-exercise social contact control in treating depression among caregivers. The effects of exercise on their cognition, quality of life and balance ability are also assessed. We will also examine if BDNF polymorphisms modulate mood changes in response to exercise intervention. Focus groups will be organised at the end to find out the facilitators and barriers in taking up exercise. The findings may offer an avenue of intervention by providing a low cost, relatively safe and effective treatment for dementia caregivers, which may in turn benefit the persons with dementia.