To investigate the effect of clinical trials on anxiety, depression, and the quality of life experienced by the family caregivers (FCs) of cancer patients.We screened the FCs of patients who were participating in clinical trials and FCs of patients who were not participating in clinical trials [group FCs-GCP (FG) and group FCs-non-GCP (FNG) at Cancer Center of West China Hospital]. We assessed the anxiety, depression, and quality of life of the FCs using the Hospital Anxiety and Depression Scale and SF-12. The demographic characteristics of FCs and patients were analyzed.The prevalences of anxiety and depression showed no significant difference between FG and FNG (46.3 vs. 51.5%, P = 0.604; 36.6 vs. 51.5%, P = 0.131, respectively). Physical Component Scores (PCS) were 48.87 ± 7.67 for FG and 48.01 ± 8.12 for FNG (P = 0.618) while Mental Component Scores (MCS) were 48.92 ± 7.78 and 44.89 ± 11.42, respectively (P = 0.031). The anxiety of FCs was positively associated with patients' advanced disease (HR 4.292 [1.409, 13.072], P = 0.010) and initial treatment (HR 3.105 [1.014, 9.515], P = 0.047). Depression was positively related to advanced disease (HR 3.347 [1.140, 9.832], P = 0.028), and negatively related to patients participating in clinical trials (HR 0.421 [0.180, 0.985], P = 0.046) and the education degree of FCs (HR 0.355 [0.149, 0.843], P = 0.019). MCS was positively associated with patients participating in clinical trials (β = 5.067, 95% CI [0.817, 9.317], P = 0.020) and negatively associated with advanced disease (β = -8.055, 95% CI [-19.804, 6.528], P = 0.002).The FCs of the cancer patients who participated in clinical trials showed a comparable worrying situation of anxiety and depression to the FCs of regular cancer patients. This indicates that more concern and attention should be given to this population, and further study on them is warranted.Copyright © 2022 Guo, Lin, Qiu, Tian and Zhu.