Background: Gemcitabine-based chemotherapy is considered as a standard front-line treatment for patients with advanced pancreatic cancer. Although addition of erlotinib or S-1 to gemcitabine has yielded better outcomes, it has showed just modest improvement in survival. To overcome this limitation, we evaluated the efficacy and safety of the combination of gemcitabine, erlotinib, and S-1 for the treatment of advanced pancreatic cancer. Methods: Chemotherapy-naïve patients with pathologically proven locally advanced, recurrent or metastatic pancreatic adenocarcinoma were assessed for eligibility. Gemcitabine at 1,000 mg/m² was administered intravenously on day 1, and 8, erlotinib at 100 mg/day was administered on days 1-21, and S-1 at 60 mg/m² was administered on days 1-14 every 21 days and continued to maximum of 8 cycles of treatment. Dose escalation of S-1 to 80 mg/m²was permitted from second cycle for pre-defined tolerable patients. Results: Thirty-seven patients (median age 61.5 years) were enrolled. A total of 140 cycles of chemotherapy were administered (median of 3.8; range 1–8 cycles). Toxicities were evaluated in 36 patients, and the responses were evaluated in 32 patients. Major grade 3/4 toxicities included neutropenia (25%), febrile neutropenia (2.8%), fatigue (22.2%), infection (8.3%), vomiting (5.6%), and mucositis (5.6%). The overall response rate was 12.5% [95% confidence interval (CI), 5.1-28.9%] and disease control rate was 71.9% (95% CI, 56.8-86.3%). The median progression-free survival and overall survival were 3.7 months (95% CI, 2.8-4.6 months) and 6.7 months (95% CI, 3.4-9.9 months), respectively. Conclusions: The combination of gemcitabine, erlotinib, and S-1 provided an acceptable toxicity profile and modest clinical benefits in patients with advanced pancreatic cancer. Clinical trial information: NCT01693419