Background: Family caregivers of dying cancer patients are affected by grief experiences and bereavement complications. Several approaches such as psycho-emotional care and an increase in spirituality have been suggested to diminish these complications. However, the knowledge about the effects of family-based dignity intervention and expressive writing on anticipatory grief in family caregivers of dying cancer patients is limited. This is a study protocol describing a hospital-based mixed-methods study on the effects of family-based dignity intervention and expressive writing on anticipatory grief in family caregivers of dying cancer patients. Methods: This mixed-methods study will be done in an embedded explanatory design with two quantitative and qualitative phases. In the first phase (quantitative), a randomized clinical trial will be done, in which 200 family caregivers of dying cancer patients will be randomly assigned to one of the four groups: family-based single dignity intervention (group 1), expressive writing intervention (group 2), combined family-based single dignity intervention and expressive writing (group 3), and control (group 4). At baseline, 1 week and 2 weeks after the interventions, anticipatory grief will be assessed by a 13-item anticipatory grief scale. After the quantitative phase, the qualitative phase will be conducted through the conventional content analysis approach of Granheim and Lundman, in which an individual semi-structured interview will be taken from participants in the first phase to collect data on their experiences on interventions. Finally, data from the quantitative and qualitative phases will be analyzed and discussed. Discussion: Family caregivers of dying cancer patients usually experience depression, anxiety, and psychological distress due to isolation and inadequate social support. Psychological interventions such as dignity and expressive writing interventions may help caregivers to obtain a better understanding of themselves and to increase their abilities to cope with caregiving difficulties. Therefore, there is a need for a comprehensive study confirming the effects of mentioned interventions on family caregivers of dying cancer patients. Trial registration: Iranian Registry of Clinical Trials (www.irct.ir) identifier: IRCT20210111050010N1. Date of trial registration: Feb 6, 2021. This is the first version of this protocol.