Background: Carbon-ion radiotherapy (C-ion RT) has the potential advantages in terms of improved dose localization and enhanced biological effectiveness compared to conventional radiotherapy or proton therapy. C-ion RT is expected to contribute to the prolongation of survival in patients with pancreatic ductal adenocarcinoma (PDAC). We started C-ion RT for pancreatic cancer at SAGA HIMAT since April 2014. The aim of this study is to evaluate the long-term clinical results of C-ion RT for locally advanced PDAC. Methods: From April 2014 to March 2018, 144 patients with pancreatic cancer were treated with definitive C-ion RT. 80 patients who were confirmed as unresectable locally advanced PDAC were included in this retrospective analysis. C-ion RT was performed with 55.2 Gy (RBE) at 12 fractions in 3 weeks. Overall survival (OS) and prognostic factors were analyzed. Toxicities were evaluated using the CTCAE ver. 5.0. Results: The median follow-up period for survivors was 38 (range 13-59) months from the initiation of C-ion RT. In all patients, planned C-ion RT was completed. Induction chemotherapy was performed in 64 patients (80%) and the median duration time was 3 (range 1-19) months. Seventy patients (86%) underwent concurrent chemotherapy with gemcitabine or S-1. 2y-, 3y-, and 4y-OS from C-ion RT were 47% (95%CI, 37-59%), 25% (95%CI,16-37%), and 18% (95%CI, 10-30%), respectively. 2y-, 3y-, and 4y-OS from initial treatment were 55% (95%CI, 45-66%), 33% (95%CI, 24-45%), and 20% (95%CI, 12-32%). Multivariate analysis showed that PS 1-2, CA19-9 ≥350, and the absence of concurrent chemotherapy were independent prognostic factors on OS. Only seven patients (9%) experienced grade 3 toxicities that were gastrointestinal ulcer/bleeding (n = 4), anorexia (n = 1), leukopenia (n = 1), and neutropenia (n = 1). There was no grade 4 or 5 toxicity. Conclusions: C-ion RT for locally advanced PDAC was effective and well-tolerated.