We report three cases of advanced gastric cancer successfully treated by combination therapy of S-1 and docetaxel (DOC). We administered S-1 orally at 80 mg/m² on days 1 to 7 and days 15 to 21, and DOC intravenously at 40 mg/m² on day 1 and 15, and evaluation was conducted every two courses. Case 1: A 73-year-old man with gastric cancer of cT4a, accompanied with bulky N2 lymph node metastasis, was treated with two courses of S-1 and DOC. Partial response was confirmed, followed by total gastrectomy, which revealed his histological grade to be 1b. Case 2: A 65-year-old man with gastric cancer of cT4a, accompanied with bulky lymph node metastasis, was treated with two courses of S-1 and DOC. Partial response was confirmed, followed by distal gastrectomy, which revealed his histological grade to be 1b. Case 3: A 76-year-old woman with gastric cancer of cT4b (panc), was treated with four courses of S-1 and DOC. After that, the main tumor was judged to be cT4a, followed by total gastrectomy, which revealed her histological grade to be 1b. Combined S-1 and DOC chemotherapy is an effective regimen for the treatment of unresectable gastric cancer.