Reminiscence therapy has been utilized for many years in the treatment of dementia in older people. Purposes of the research included examining different methods of promoting interactivity, social participation, cognitive function improvement in those with dementia, and the effectiveness in reducing symptoms of depression following group treatment. This study used pretest and posttest electroencephalography (EEG) measurements to test reminiscence therapy efficacy on participants. This research organized a social group work with 12 elderly clients with dementia (mild to moderate stage) selected from among 90 residents of an older persons care facility in Pingtung. Eleven agreed to join the study, and 10 completed successfully all treatment sessions. Eight sessions of reminiscence cooking lessons were conducted. The effectiveness of interventions was evaluated by comparing presession and postsession EEG, mental health status, depression scale, and feeling of participation scale scores. Significant differences in values, particularly for EEG, were found between the two sets of scores. The average value of participants' fast waves rose from 43.88 to 55.12, whereas average slow-wave values fell from 56.12 to 44.13. After analysis using the Wilcoxon matched paired signed rank test, significant differences were noted. Findings and suggestions include the following: (a) The rise in Mini-Mental State Examination and reduction in depression scale scores, although noted, were not significant, and (b) the self-achievement, emotional stability, family atmosphere, and physical needs of participants were met. The authors recommend that reminiscence group work be promoted in the home for older persons and that childhood cooking sessions twice each week may be the ideal format for reminiscence group work.