Objective: To explore the clinical efficacy of S-1 single agent adjuvant chemotherapy for the patients undergoing radical resection of extrahepatic biliary carcinoma. Methods: The clinical data of 108 patients with extrahepatic biliary carcinoma receiving radical resection who were admitted from January 2014 to June 2017 were retrospectively analyzed. There were 62 males(57.4%)and 46 females(42.6%),with a median age of 59 years (range:26 to 79 years),10 cases(9.3%) in stage Ⅱ,85 cases(78.7%) in stage Ⅲ, and 13 cases (12.0%) in stage Ⅳ, 40 cases(37.0%) of hilar cholangiocarcinoma, 8 cases(7.4%) of middle cholangiocarcinoma, 25 cases (23.2%) of distal cholangiocarcinoma, 35 cases(32.4%) of gallbladder carcinoma.After radical resection of extrahepatic biliary carcinoma, 49 patients receiving S-1 single agent chemotherapy and 59 patients receiving non-special treatment were divided into the chemotherapy group and the operation group,respectively. All the dates of the patients were followed up and collected with the overall survival time,tumor-free survival time,1,2 and 3-year survival rate after operation,and the rate of major toxic reaction during chemotherapy of the chemotherapy group. Survival curve was drawn by the Kaplan-Meier method, and survival analysis was done using the Log-rank test. Results: There were no significant differences in the general date of two groups(sex, age, tumor size, tumor site, TNM stages, degree of differentiation). The median overall survival time and the median tumor-free survival time in the chemotherapy group were 27 months and 21 months,respectively,and in the operation group were 21 months and 17 months,respectively. There were differences between the two groups in the overall survival rates(chi(2)=3.967,P<0.05) and the 2 and 3-year survival rate(63.3%,36.6%;41.6%,20.4%;chi(2)=4.510,P<0.05;chi(2)=6.143,P<0.05),but the 1-year overall survival rate (83.4%,79.7%)was not statistically significant(chi(2)=0.286,P>0.05). There were no significant differences in the tumor-free survival time,1,2 and 3-year tumor-free survival rate(77.6%,41.4%,33.1%;62.7%,30.9%,21.2%)between the two groups(chi(2)=0.876,P>0.05;chi(2)=0.252,P>0.05;chi(2)=1.571,P>0.05;chi(2)=3.323,P>0.05,respectively). The main toxic reaction during chemotherapy were dyspepsia(28.6%, 14/49), anemia(26.5%, 13/49), and leukopenia(22.5%, 11/49), all of which were mild. Conclusion: S-1 single agent chemotherapy after radical reseetion of extrahepatic biliary carcinoma could effectly improve the survival of patients and all of the main toxic reaction during chemotherapy were mild.