This review is concerned with the usefulness and the problem of biomarkers for cancer of digestive organs. Carcinoembryonic antigen (CEA) is a most popular and useful tumor marker for cancer of digestive organs. Squamous cell carcinoma (SCC) antigen and CYFRA have been reported as a useful tumor marker for esophageal cancer. CEA and CA 19-9 are a good prognostic factor in gastric cancer patients. The post-operative increase of serum CEA can be a predictive marker for the patients of colorectal cancer. Development of a radioimmunoassay for highly sensitive detection of tumor markers, they are considered to be useful for monitoring after treatment. But are not useful for the early diagnosis. The diagnosis of hepatocellular carcinoma (HCC) is based mainly on serological markers, such as alpha-fetoprotein and PIVKA-II. The two are useful complementary markers of HCC because they do not correlate with each other. But the problem of the false-positive rate for the patients with chronic hepatitis or liver cirrhosis is still remained. A typical marker of pancreatic and bile duct cancer is carbohydrate antigen, but the sensitivity of these markers is only 50%. Recent molecular biological analysis may be used as effective biomarkers in the diagnosis, prognosis, therapy, and risk assessment of digestive cancer.