Physical activity is linked to benefits such as increased physical fitness, cognition, emotional and social functioning, general health and well-being in older people. Some evidence suggests that this also applies to people living with dementia. However, it can be harder for them to perform physical activities, due to several barriers, such as issues with orientation and balance problems. A relatively new type of physical activity called exergaming may help them overcome these barriers. Exergaming is "physical exercise interactively combined with cognitive stimulation in a gaming environment". The aim of our study is to evaluate the effectiveness and cost-effectiveness of exergaming compared to regular activities in people living with dementia, who attend day-care centres. Additionally, we want to investigate whether the exergaming activity for the person living with dementia, also (indirectly) affects the informal caregiver, as well as which facilitators and barriers to implementation of exergames for this target group exist.A cluster Randomized Controlled Trial (RCT), with economic and process evaluations alongside will be carried out. In the Netherlands, 24 day-care centres are randomized in the experimental or control group. The study group will consist of 224 dyads (community-dwelling participants with dementia and their informal caregivers), who are interviewed at baseline, and at 3 and 6 months of follow-up. The participant with dementia has to visit the day-care centre for at least two days per week, have a diagnosis of mild to moderate dementia and have an informal caregiver present, who is willing to participate. Societal cost data will be collected during interviews, using healthcare utilization diaries, and from day-care centres. The process evaluation will only involve the experimental group, and will include an online survey, qualitative interviews and focus groups.This study will contribute to the evidence base that more effective exercise among people with dementia will result in positive effects on their wellbeing and quality of life. This will motivate people with dementia to be physically active. We also envision that there might be a positive effect on the burden of care experienced by their informal caregivers.This trial was registered at the Netherlands Trial Register (NTR) on December 10, 2015 (number: NTR5537 ), this publication is based on protocol amendment number 01, issue date 28 December 2018. This includes all items from the World Health Organization Trial Registration Data Set [see Additional file 1].