Background: Despite the significant physical, emotional, and financial burdens faced by the families of cancer patients, such as caregiving, assisting with hospital visits, and supporting social activities, research on their quality of life (QOL) remains insufficient. Objective: To evaluate the QOL of the families of patients undergoing chemotherapy for cancer and to investigate its relationship with the patients' treatment courses. Methods: A prospective analysis was conducted using EORTC-QLQ-C30 to measure the QOL of patients with unresectable or recurrent solid tumors and their families. Assessments were performed before first-line treatment and before second-line treatment in patients treated at our department between 2016 and 2024. Changes in QOL over the treatment periods and the impact of treatment efficacies were examined. Results: A total of 45 patients were included. Family members frequently reported fatigue, pain, insomnia, and financial difficulties both before and after treatment. Emotional and cognitive functioning declined to the same extent as in patients and did not recover over time. Social functioning notably reduced during the early treatment phase. Treatment efficacy had no impact on the QOL of family members. Discussion: The survey using self-administered questionnaires revealed the consistent need for emotional support for families and highlighted the importance of early social support during the treatment phases.