BACKGROUND: The technique to analyze circulating tumor DNA (ctDNA) in body fluid (so-called "liquid biopsy") is recently developed. AIMS: Our aim was to assess the utility of liquid biopsy for predicting progression of pancreatic ductal adenocarcinoma (PDAC) after surgical resection or chemotherapy. METHODS: A total of 72 patients with PDAC were retrospectively enrolled for this study, 33 treated surgically and 39 given chemotherapy, either FOLFIRINOX (oxaliplatin/irinotecan/fluorouracil/leucovorin) or gemcitabine plus nab-paclitaxel. Prior to treatment, patients were screened for the presence of KRAS mutations (G12D and G12V) in plasma using droplet digital polymerase chain reaction, and outcomes were compared. RESULTS: KRAS mutations were identified in plasma samples of 12 patients (36%) underwent surgical resection. Patients with plasma KRAS mutations had significantly shorter disease-free survival (DFS) and overall survival (p < .01 and p = .01, respectively). Of 10 clinical variables analyzed, plasma KRAS mutation was the factor predictive of DFS in multivariate analysis (RR = 3.58, 95% CI: 1.36-9.60; p = .01). Although 12 patients (31%) given chemotherapy tested positive for plasma KRAS mutations, there was no demonstrable relation between plasma KRAS mutations and progression-free survival (PFS) or overall survival (OS) (p = .35 and p = .68, respectively). CONCLUSIONS: In patients with PDAC, detection of KRAS mutations in plasma proved independently predictive of early recurrence after surgical resection but did not correlate with PFS following chemotherapy.