Purpose: The purpose of this study was to identify the effects on cognitive function, mood, problematic behaviors and response to interaction with robot pet by elderly people with dementia. Method: A methodological triangulation design with quantitative and qualitative methods was used. The participants were 9 elderly people with dementia. The intervention was conducted twice a week for 4 weeks, Qualitative data were collected by interviews and video-taping for analysis of the responses of participants, Results: 1) Cognitive function, mood and problematic behaviors did not show any significantly differences after the program. 2) Analysis of the responses showed increases in verbal communication and positive action. Conclusion: The robot pet program had positive effects such as increasing communication and interaction. Therefore, this program could be considered as an effective program for emotional support for elderly people with dementia. However further repetitive study is need to validate the result.