Aim. To detect the expression of dual oxidase (DUOX) 2 in Barrett esophagus, gastric cancer, and colorectal cancer (CRC). Materials and Methods. The endoscopic biopsies were collected from patients with Barrett esophagus, while the curative resection tissues were obtained from patients with gastric cancer, CRC, or hepatic carcinoma. The DUOX2 protein and mRNA levels were detected with immunohistochemistry (IHC) and real-time quantitative PCR (qPCR). The correlation of DUOX2 expression with clinicopathological parameters of tumors was identified. Results. Low levels of DUOX2 mRNA were detected in Barrett esophagus and the adjacent normal tissues, and there was no difference between these two groups. DUOX2 protein was found in Barrett esophagus and undetectable in the normal epithelium. The DUOX2 mRNA and protein levels in the gastric cancer and CRC were increased compared to the adjacent nonmalignant tissues. The elevated DUOX2 in the gastric cancer was significantly associated with smoking history. In CRC tissues, the DUOX2 protein expression level in stages II-IV was significantly higher than that in stage I. In both hepatic carcinoma and the adjacent nonmalignant tissue, the DUOX2 was virtually undetectable. Conclusion. DUOX2 in Barrett esophagus, gastric cancer, and CRC may be involved in the tumorigenesis of these tissues.