Family caregivers play a critical role in dietary care and the nutritional status of people with dementia. The aim of this study was to investigate the effects of a family care-based dementia dietary educational program (DDEP) on family caregivers’ nutritional knowledge, healthy eating behavior and nutritional status of people with dementia. A total of 57 pairs of participants completed this longitudinal experimental study. Group A received routine care. Group B received the DDEP. Three outcomes were measured at pretest (T1), posttest (T2) and follow-up test (T3). Generalized estimating equations and regression were used to analyze the data. The scores of the caregivers’ nutritional knowledge significantly increased after receiving the DDEP in group B, and this increase was better than in group A. The posttest and follow-up test scores of healthy eating behavior were significantly higher than the pretest scores in both groups. The scores of nutritional status in group B increased from the pretest to the follow-up test, although there was no significant difference between the two groups. Some demographic factors played significant roles in the caregivers’ nutritional knowledge and healthy eating behavior. In sum, the DDEP improved the caregivers’ nutritional knowledge and healthy eating behavior for dementia. The demographic factors of family caregivers should be considered when providing nutritional information to enhance the nutritional status of people with dementia. The DHPDEP should be incorporated into the in-service education and training courses for nurses or dietitians who work with people with dementia.