Background: Arctigenin, which is abundant in the seeds of Arctium lappa Linné, was found by a novel strategy to attenuate cancer cells’ tolerance to glucose deprivation (antiausterity) and showed antitumor activity in mouse xenograft models. GBS-01 is an orally administered drug and contains rich arctigenin extracted from Arctium lappa Linné, which is one of the traditional herbal medicine. This study investigated the maximum-tolerated dose of GBS-01 based on the frequency of dose-limiting toxicities (DLT) in patients with refractory advanced pancreatic cancer, which is considered as one of the hypoxic cancer. Methods: Histologically or cytologically proven advanced pancreatic adenocarcinoma patients refractory to gemcitabine were enrolled. GBS-01 was administered orally at escalating doses from 3g to 12g qd. DLT was defined as grade 4 hematological toxicities and grade 3 or 4 non-hematological toxicities during first 28 days of the treatment. Response evaluation based on RECIST criteria and progression-free survival were set as secondary endpoint for efficacy evaluation. Results: Fifteen patients (GBS-01 3g: 3 patients, 7.5g: 3 patients, 12g: 9 patients) were enrolled in this trial. All patients were refractory to S-1 as well as gemcitabine. All patients at the three dose levels did not demonstrate any sign of DLT. The main adverse events of this agent were increased γGTP, hyperglycemia, and increased total bilirubin, but all toxicities were extremely mild. Of all 15 enrolled patients, 1 patient showed a partial response and 4 patients had a stable disease. The median progression-free and overall survival time for all patients were 1.05 months and 5.68 months, respectively. Conclusions: The recommended dose of GBS-01 was 12 g qd (4 g as a extract of Arctium lappa Linné), and favorable clinical responses were obtained. A multicenter phase II trial is being planned to evaluate the efficacy and safety of this agent. Clinical trial information: 000005787.