The safety and effectiveness of chemotherapy in elderly patients with biliary tract cancer (BTC) remain unclear. Therefore, we retrospectively reviewed patients who underwent chemotherapy for locally advanced, metastatic, or recurrent BTC at our institution from January 2016 to December 2021. Of the 283 included patients, 91 (32.5%) were aged 75 years or older when initiating chemotherapy. Elderly patients were more likely than non-elderly patients to receive monotherapy with gemcitabine or S-1 (58.7% vs. 9.4%, p < 0.001) and were less likely to experience grade 3–4 toxicities (55.4% vs. 70.2%, p = 0.015). The rates of termination due to intolerance (6.5% vs. 5.8%, p = 0.800) and transition to second-line chemotherapy (39.1% vs. 40.3%, p = 0.849) were similar between groups. In the overall cohort, age was not an independent predictor of overall survival (OS). Within the elderly cohort, there were no differences in severe adverse events between patients receiving monotherapy and combination therapy (50.0% vs. 63.2%, p = 0.211). Median OS was longer in the combination therapy group (10.4 vs. 14.1 months; p = 0.010); however, choice of monotherapy was not an independent predictor of overall survival. Monotherapy appears to be a viable alternative in selected elderly BTC patients.