Background: The ageing of people with intellectual disabilities, involving consequences like dementia, creates a need for methods to support care staff. One promising method is Dementia Care Mapping (DCM). This study examined the effect of DCM on job satisfaction and care skills of ID-care staff. Methods: We performed a quasi-experimental study in 23 group homes for older people with intellectual disabilities in the Netherlands. Among staff, we assessed job satisfaction and care skills as primary outcomes and work experience measures as secondary outcomes (N = 227). Results: Dementia Care Mapping achieved no significantly better effect than care as usual (CAU) for primary outcomes on job satisfaction (MWSS-HC) and working skills (P-CAT). Effect sizes varied from -0.18 to -0.66. We also found no differences for any of the secondary outcomes. Conclusion: Dementia Care Mapping does not increase job satisfaction and care skills of staff caring for older people with intellectual disabilities. This result differs from previous findings and deserves further study.