Aim: To validate the de Morton Mobility Index (DEMMI) in community-dwelling older adults who require informal care. Methods: Thirty-five consecutively recruited older adults (>65 years) living in the community who required informal care were included from Melbourne and regional Victoria, Australia. Participants were assessed using a battery of questionnaires, the Falls Risk for Older People (Community version), modified Barthel Index, Geriatric Depression Scale, the Medical Outcomes Survey Short Form 36, the Assessment of Quality of Life and the DEMMI. The DEMMI consists of 15 mobility items that are administered by therapist observation of physical performance. Each participant was assessed in their home. Results: The DEMMI is without floor or ceiling effects for community-dwelling older adults who require informal care, and evidence of convergent, discriminant and known groups validity was obtained for the DEMMI. DEMMI data fitted the Rasch model and the minimal clinically important difference was 11 points. Conclusions: The DEMMI has suitable clinimetric properties for application in community-dwelling older adults who require informal care.