Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers worldwide and is difficult to detect at its early stages when treatment is most effective. Therefore, we performed a comparative proteomic study to identify new biomarkers for the detection of PDAC.Serum samples from patients with PDAC, chronic pancreatitis and normal controls were compared using two-dimensional difference gel electrophoresis (2D-DIGE). Differentially expressed separated proteins were subsequently identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF/TOF-MS). Then, transthyretin (TTR), one of the differentially expressed proteins, was validated through real-time PCR, western blot and immunohistochemistry. Finally, enzyme-linked immunosorbent assays (ELISA) were employed to confirm the levels of transthyretin in the sera.A total of 21 protein spots showed greater than 1.5-fold changes in expression level in the sera from PDAC patients compared with the normal controls. Among the identified proteins, validation experiments verified the differential expression of transthyretin in PDAC tissue, confirming the proteomic data showing that transthyretin was significantly elevated in patients with PDAC. The ELISA results revealed that the sensitivity and specificity for TTR and CA19-9 in distinguishing PDAC patients from normal individuals were 90.5, 47.6, 66.7 and 85.7 %, respectively, and 81.0 and 85.7 % for their combination.These results suggest that the level of transthyretin is elevated in patients with PDAC. In combination with CA19-9, transthyretin may provide additional information for the detection of PDAC and should be further investigated.