There is no disease-specific instrument to measure the quality of life of significant others of cancer patients in Germany. In this study, we evaluated the reliability and construct validity of a German version of the Caregiver Quality of Life Index-Cancer (CQOLC) in a sample of 212 caregivers of breast and gynaecologic cancer patients. The CQOLC was administered along with the World Health Organization Quality of Life short version (WHOQOL-BREF) to caregivers of patients taking part in a randomized-controlled intervention study. Data of 212 caregivers were gained at the baseline of the study. Internal consistency was determined by Cronbach’s α. Construct validity was examined by conducting a confirmatory factor analysis (CFA) and hypothesis testing. Correlations between change scores with patients’ global health-related quality of life (HRQoL) were calculated for three time points to evaluate the responsiveness. The three subscales “burden”, “disruptiveness”, and “financial concerns” indicate to a good reliability of the instrument (Cronbach’s α ranged between 0.754 and 0.832), while the subscale “positive adaptation” demonstrated low reliability ( α = 0.579). A CFA based on data from the whole set of CQOLC items resulted in CFI levels < .90, and a CFA without problematic items resulted in CFI levels also < .90. The construct validity of the CQOLC could be approved by a moderate to high convergence with close variables as the global HRQoL. Mean differences between caregivers of curatively or palliatively treated patients were nonsignificant ( p = 0.959) at T1. Correlations for responsiveness were low with correlation coefficients ranging from 0.030 to 0.326. These data indicate that additional research is needed to further verify the validity of the instrument. The German scale of the CQOLC might be appropriate for clinical and research use, if the wording of some items is refined and if content validity is also assessed by caregivers themselves. The assessment of cancer patients’ caregiver’s quality of life can contribute to a better understanding of the effects of patient-oriented interventions including also closely involved next of kin’s around the cancer patients.