Background: Families of patients with organ transplants experience many problems, both with the onset of illness and during the hospitalisation of their relative for an organ transplant. The healthcare providers try their best to give high-quality care to patients. However, they neglect quality of life and psychosocial needs of family caregivers. Aims: This study aimed to assess the psychosocial needs and quality of life of the family caregivers of post-transplant patients and the relationship between these two variables. Methods: This descriptive correlational study was conducted on liver, kidney and bone marrow transplant wards in the largest transplant centre affiliated with a university of medical science in south-eastern Iran. The sample included 230 family caregivers of post-transplant patients, who were selected using quota sampling. Data were collected using the 45-item questionnaire of psychosocial needs (the Critical Care Family Needs Inventory) with five dimensions (assurance, comfort, information, proximity and support), and the Short Form-36 Quality of Life questionnaire with eight scales (physical functioning, physical problems, emotional problems, social functioning, pain, vitality, mental health and perception of health). In the Critical Care Family Needs Inventory, 1 indicates not important and 4 very important. In the Short Form-36 Quality of Life questionaire, 0 indicates the worst health and 100 the best health. Results: The participants rated the mean of their psychosocial needs as important (3.18 ± 0.27). Also, the mean of quality of life of participants was at an undesirable level (45.17 ± 92.66). The psychosocial needs of the caregivers showed a poor, inverse significant relationship with their quality of life (r = −0.16, p = 0.01). Conclusion: The results showed that with increasing psychosocial needs of family caregivers of post-transplant patients, their quality of life declines. Healthcare providers should implement developed plans and appropriate strategies to fulfil psychosocial needs and improve the quality of life of family caregivers of these patients.