Objective Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative treatment associated with high morbidity and mortality. It is often necessary for family caregivers to become highly involved in the care, especially when patients return home after a long period of inpatient care. Family caregivers' preparedness for the tasks and demands of the caregiving role prior to allo-HSCT might help them during this distressing time. The aim of this study was to explore whether demographic factors are associated with preparedness for caregiving prior to allo-HSCT and if such preparedness for caregiving is associated with caregiver outcomes in terms of caregiver burden, anxiety/depression, competence, self-efficacy, and general health among family caregivers. Method This correlational cross-sectional study included 86 family caregivers of patients to undergo allo-HSCT, who completed a self-administered questionnaire on preparedness, caregiver burden, anxiety/depression, competence, self-efficacy, and general health. Descriptive statistics and multiple regression models (linear and ordinal) were used to analyze the data. Results Family caregivers with a higher education and those who were the patient's partner were significantly associated with a higher level of preparedness for caregiving, while gender and age were not significant. Higher preparedness was significantly associated with higher competence and self-efficacy and lower symptoms of depression, even after the model was adjusted for education, relationship to the patient, gender, and age but not for anxiety or caregiver burden. Higher levels of preparedness were also significantly associated with better general health. Significance of results A higher level of preparedness for caregiving prior to allo-HSCT was associated with better family caregiver outcomes. Assessing family caregivers prior to allo-HSCT to identify those with insufficient preparedness might enable the provision of individually tailored psycho-educational support to help them cope with their caregiving role and prevent potential negative consequences.