S-1 is the prodrug of 5-fluorouracil (5-FU), comprised of tegafur, gimeracil (dihydropyrimidine dehydrogenase inhibitor) and oteracil (the inhibitor of phosphorylation in gastrointestinal tract) with a ratio of 1:0.4:1. The first phase II clinical trials showed good clinical efficacy with S-1.Moreover, Ueno et al. identified better objective response rates with S-1 than those with gemcitabine. Besides, S-1 is not inferior to gemcitabine regarding to overall survival rates and progression free survival rates. And significant improvement of progression free survival rates can be achieved by combination of S-1 and gemcitabine. There was no difference between incidence rates of adverse effects of S-1 and gemcitabine, with more gastrointestinal toxicities with S-1 while more hematologic toxicities with gemcitabine. Therefore, S-1 is an alternative for treating locally advanced or metastatic pancreatic cancer, especially for those resistant to gemcitabine. Although there are no phase III studies on S-1, phase II studies have already shown better disease control rates (52%-58%), median overall survival time (4.5-6.3 months) and tolerable adverse effects in advanced pancreatic cancer resistant to gemcitabine treated with S-1.