The global cost of dementia is over 818 billion, and a further rise is expected in the next decade. While family caregiving is the backbone of the formal care service, promoting living well with dementia needs to extend to a dyadic perspective to address the needs of persons with dementia and their caregivers. Unique to dementia caregiving, imbalanced exchange in the assistance, interaction, relationship and autonomy between the partners in a care dyad always challenges their social interaction and relationships. Such eroding dyadic dynamics not only worsens the mental health of caregivers, but also compromises the quality of caregiving, fosters more dementia deterioration, and eventually complicates the caregiving process. Nevertheless, least attention is directed to dyadic dynamics in promoting living well with dementia. Partner exercise is designed in a way which requires collaboration of two members to enable the workout of each other. In addition to the benefits of exercise on dementia symptom control and caregiver's stress management, partner exercise provides a meaningful encounter to encourage reciprocity, collaboration and relationship closeness within the care dyad. This study aims to examine whether a 16-week theory-based partner exercise, named as Buddy-Up Dyadic Physical Activity (BUDPA) program, can improve dyadic dynamics and health outcomes of care dyads of mild to early-moderate dementia. This sequential mixed-method study will recruit 111 care dyads from the elderly centers in Hong Kong. They will be randomized to receive the enhanced BUDPA program or usual care. The changes in the dyadic dynamics and health outcomes \[including symptom severity and health-related quality of life (HRQL) of persons with dementia; and affect, positive aspects of caregiving and HRQL of family caregivers\] between the two study groups from baseline (T0) to 16-weeks after baseline (T1) upon completion of the training , and at 24-weeks after baseline (T2). Data from outcome evaluation and interviews will be integrated to solicit a thorough understanding on the impact of BUDPA. This study marks the first attempt to use theory-driven dyadic intervention to enhance the dyadic dynamics and health outcomes of dementia care dyads. The project will advance the dyadic science in a dementia caregiving context and inform the development of evidence-based care model in dyadic fashion to promote living well with dementia in a caregiving context.