Objective: To investigate the quality of life (QoL) and the impact of caregiving in family caregivers of hematological cancer patients and its association with patient symptom burden. Methods: A cross-sectional study including Danish patients (n = 375) and caregivers (n = 140). Caregivers completed scales for anxiety and depression using the Hospital Anxiety and Depression Scale, sleep quality using the Pittsburgh Sleep Quality Index, health related QoL using the 12-item Short-Form Health Survey, and caregiver roles using the Caregiver Roles and Responsibilities Scale. Patients reported symptoms using the MD Anderson Symptom Inventory. Analysis of covariance was used to examine associations between patient symptom burden and caregivers' QoL outcomes. Results: The results show that caregivers experience sleep difficulties, moderate anxiety, and reduced QoL. Patient symptom burden was significantly associated with caregiver anxiety (p = 0.009), and mental well-being (p = 0.002), while patient treatment status was a significant factor associated with caregiver anxiety (p = 0.016), depression (p = 0.009), emotional well-being (p = 0.002), and sleep (p = 0.01). Conclusion: Caregivers of patients with hematological cancers undergoing active treatment face a high symptom burden, which significantly impacts their QoL, including sleep, psychological well-being, and emotional health. Patients reported a high symptom burden, and patient symptom burden was significantly associated with caregiver QoL. Adequate patient and caregiver support is needed to promote their well-being and mitigate adverse health effects in caregivers, and this should be acknowledged in the context of caring for patients with hematological cancer.