Objectives Older spouses are a significant part of family caregivers of patients with Alzheimer’s disease (AD) and need support. Evidence suggests that different factors influence the support of older spousal caregivers. However, there is little evidence about these factors in developing countries like Iran. This study aimed to identify the factors affecting the support of Iranian older spousal caregivers of people with AD. Method This qualitative study used Graneheim and Lundman’s conventional content analysis approach. Through purposive sampling, 10 caregivers, three family members, and three professionals were recruited from various cognitive clinics and centers. In-depth and semi-structured interviews were used to collect data and continued until conceptual saturation was achieved. Results Two themes were derived from the data as factors affecting support, which included (1) caregiver’s support-seeking (complexity of the patient’s condition, caregiver’s geriatric health, the burden of caring for a spouse with AD, marital bond quality, caregiver’s support-phobic beliefs, caregiver’s awareness of care) and (2) capacities of support resources (supportive family, supportiveness of society, formal systems’ capability to provide support services). Conclusion The present study provided practical information about the factors influencing the support of older spousal caregivers. Healthcare providers and policymakers can use these concepts to improve the support process by strengthening caregivers’ support-seeking motivation and enhancing capacities in support resources.