Serum CA19-9 is one of the markers most frequently detected in the diagnosis and biliopancreatic diseases. The levels of CA19-9 are important for the diagnosis, treatment and prognosis of biliopancreatic diseases. With the development of medical technology, the comprehension of the value of serum CA19-9 is more and more thoroughly. The benign and malignant diseases of biliopancreatic systems can be differentiated by the variation of the values of serum CA19-9, which has high sensitivity in malignant tumors. Serum CA19-9 is one of the independent indicators for evaluation of resectability of tumors and the survival time and life quality of the patients. In this article, the significance of serum CA19-9 in the diagnosis, treatment and prognosis evaluation for biliopancreatic diseases were reviewed.