Early detection of cancer and the monitoring of cancer recurrence in treated patients are significant challenges in esophageal squamous cell carcinoma (ESCC). Liquid biopsy is the identification of tumor biomarkers from minimally invasive samples of biological fluids, including urine, blood, stool, saliva, or cerebrospinal fluid. Liquid biopsy offers a potential solution to the problems of detection and surveillance as DNA shed from cancer cells as cell-free DNA or in exosomes can be detected in body fluids. By detecting these DNAs, we can identify the presence of cancer-associated mutations for basic detection, as well as to obtain information on the recurrence and evolution of disease following initial treatment. These sources of information have the potential to significantly improve the management of patients with ESCC. In this chapter, we detail a method for the isolation of cell-free DNA from blood plasma and DNA associated with exosomes in blood from patients with esophageal squamous cell carcinomas.