The purpose of this research was to observe the relationships between sociality of the demented elders and horticultural activities of group therapy. The observation paper written by social worker were used for examining the interpersonal relations and communication skills indicating sociality. The important observation results were as follows. First, interpersonal relations and communicative ability among the demented elders were generally improved by horticultural activities of group therapy. Second, horticultural activities of group therapy was especially effective in the demented group of the buddy system. The buddy system meant that each group was consisted of a pair of the same sex or the different sex on the therapeutic horticultural activities. Third, in particular, the groups composed of the different sex seemed to have more effective influence on human relationships and communication than those of the same sex. In conclusion, horticultural therapy could improve their sociality of its participants. Especially, therapeutic horticultural activities of buddy system composed of different gender seemed to have the most effect on the adaptive behavior and communicative ability among the elderly dementia.