Background: We evaluated the efficacy and safety of a modified FOLFIRINOX regimen for chemotherapy-naïve patients with metastatic pancreatic cancer. Methods: Patients with untreated metastatic pancreatic cancer (MPC) received modified FOLFIRINOX (intravenous oxaliplatin 85 mg/m2, irinotecan 150 mg/m2, 5-FU infusion 2400 mg/m2 over 46 h, no bolus 5-FU). The primary endpoints were overall survival and the incidence of grade 3 or higher neutropenia. No patients received prophylactic pegfilgrastim. Results: Sixty-nine pts. were enrolled from 39 institutions in Japan. The median overall survival was 11.2 months [95% confidence interval (CI) 9.0–]. The median progression-free survival was 5.5 months (95% CI 4.1–6.7). The response rate was 37.7% (95% CI 26.3–50.2), and the disease control rate was 78.3% (95% CI 66.7–87.3). The incidence of grade 3 or higher neutropenia was 47.8%. Serious adverse events occurred in six patients (8.7%). All AE proportions were less than those in the previous Japanese full-dose phase II study. One patient died due to interstitial pneumonia related to treatment. Conclusion: This is the first prospective study of modified FOLFIRINOX in Asia. Modified FOLFIRINOX in this study has an improved safety profile with maintained efficacy in MPC without prophylactic pegfilgrastim.