Although horticultural therapy has been used successfully to reduce neuropsychiatric symptoms in elderly people with cognitive impairment, we do not yet know how it affects balance. The aim of our study was to determine the acceptability and effect of a 12-week horticultural therapy on balance and walking speed among institutionalized older adults with cognitive impairment. This mixed-methods controlled trial included 23 participants. Subjects in the experimental group (n=13) participated in a 60 min horticultural therapy programme twice a week for 12weeks in addition to the institution's usual social activities. Subjects in the control group (n=10) participated in the institution's usual social activities. Static and dynamic balance were measured with the Performance Oriented Mobility Assessment scale. In addition, gait speed was measured. Qualitative data were collected through a semi-structured interview with participants of the experimental group. At the end of the intervention period, the experimental maintained their baseline performance on the static balance, while the control group showed a decline. The gait speed of the experimental improved, while that of the control group did not change. In dynamic balance, no changes were demonstrated. The results of our qualitative data analysis indicate that horticultural therapy increases the possibility of social interactions, encourages older people to engage in conversation. As a conclusion, horticultural therapy should be more widely included in programmes for older people with cognitive impairment.