The purpose of this research was to use the broaden-and-build theory of positive emotions as a framework to explore the positive emotions and their expansion mechanisms experienced by the elderly with moderate dementia in expressive art activities. Research method: A qualitative single case study method was used. The expressive art activities were designed with the broaden-and-build theory of positive emotions. Data collection included individual interviews with participants, observation records, individual events, and observations. All data were analyzed according to the framework approach. The results were (1) Savoring the past: The topic of “home” created a sense of friendliness and trust; (2) Positive emotions in the present: Colors induced freshness, Completing the work brought a sense of accomplishment; (3) Expanding flexible expressions and active actions; (4) Building psychological resources: Satisfied with artistic activities, and able to give and give back.