The purpose of this study was to verify effects of group language therapy based on theatre activities on communication abilities of nursing home patients with dementia. Three nursing home patients with dementia have participated to this theatre-based group language therapy. All of therapy processes were registered and analyzed. We have collected data of three types: spontaneous utterances in warm up, and narrative discourses in individual experience activities and in theatre activities. These data were analyzed by discourse elements such as C-unit, NTW, NDW, number of syllables, and topic maintenance. According to t-test result, in spontaneous utterances during warm up, NTW and NDW significantly increased after the therapy. In narrative discourses of two types’ activities, the mean scores of C-unit, NTW, NDW, number of syllables increased, but these changes were not statistically significant except the number of syllables. These findings indicate that theatre based group language therapy can be useful for improving communication abilities of elderly persons with dementia.