Background: In locally advanced, resectable gastric or gastro-oesophageal junction (EGJ) adenocarcinoma, perioperative the docetaxel-based triplet FLOT (fluorouracil plus leucovorin, oxaliplatin and docetaxel) is the standard chemotherapy in Europe. However, there is no evidence of neoadjuvant chemotherapy for resectable gastric cancer in Japan. Therefore, we conducted a phase II trial of neoadjuvant chemotherapy with docetaxel plus oxaliplatin, and S-1 (DOS) for locally advanced, resectable gastric or EGJ adenocarcinoma. Methods: Eligible patients had histologically confirmed gastric or EGJ adenocarcinoma of a clinical Stage III according to the 14th Edition of Japanese Classification of Gastric Carcinoma. DOS was administered for two or three preoperative cycles followed by eight postoperative cycles of S-1. Each 3-week cycle of DOS consisted of docetaxel 40 mg/m² and oxaliplatin 100 mg/m² on day 1 plus S-1 80-120 mg/body on days 1 to 14. Primary endpoint was 3-year progression-free survival rate, and secondary endpoints included overall survival, progression-free survival, response rate, histological response rate, R0 resection rate, and adverse events. Results: Of 50 enrolled patients, 48 (37 gastric and 11 EGJ) were eligible for the analysis. 42 (88%) patients completed two or three preoperative cycles of DOS. The most common grade 3-4 adverse events of DOS were neutropenia (69%), leukopenia (56%), diarrhea (19%), and febrile neutropenia (13%). Of 45 patients who underwent gastrectomy, postoperative morbidities (Clavien-Dindo ≥Grade II) occurred in 12 (27%) patients. R0 resection could be achieved in 43 (90%) patients. 12 (27%) and 30 (67%) of 45 patients achieved pathological response rate of Grade2-3 and Grade1b-3, respectively. There was no treatment-related death. Conclusions: Neoadjuvant DOS for locally advanced, resectable gastric or EGJ adenocarcinoma might be favorable. Long-term results will be published in two years. Clinical trial information: 000017652.