This study aimed to verify the effects of an 8-week customized program conducted at day and night care centers on cognitive function improvement in older adults with mild dementia and to exploratively analyze patterns of change according to gender. The study employed a single-group pre- and post-test design, and the participants were 22 users (11 men and 11 women) of a day and night care center located in C City, Chungcheongnam-do. The customized program was conducted four times a week for 8 weeks, with each session lasting 60 minutes, for a total of 32 sessions, and consisted of multi-domain cognitive stimulation activities including music, art, reminiscence, and manipulative activities. The same structure was applied to all participants, but the difficulty and intensity of the intervention within activities were adjusted according to performance levels. The results showed that after participating in the customized program, cognitive function of all participants significantly improved compared to pre-intervention. In the analysis within gender groups, significant improvement was observed in the male group, whereas the female group showed a tendency of improvement but without statistically significant differences. Additionally, no significant differences were observed in the amount of change between gender groups. This study confirmed that a customized program can be effectively applied to improve cognitive function in elderly people with mild dementia, and it could provide basic data for future program operation in day and night care centers and for approaches considering gender characteristics.