Gastric cancer ranks high in terms of morbidity and mortality worldwide. Multimodal therapy is therefore essential for locally advanced gastric cancer. Recent studies have demonstrated that both perioperative chemotherapy and neoadjuvant chemoradiotherapy can improve the prognosis of patients. However, the completion rate of chemotherapy after surgery remains low, which may affect survival. Thus, identifying the best way to combine radiotherapy, chemotherapy and surgery is important. The aim of this study was to explore the toxicity and efficacy of the total neoadjuvant therapy modality for locally advanced gastric cancer.This study will be a prospective, multicenter, single-arm, phase II clinical trial. Patients diagnosed with locally advanced (stage cT3-4 and cN positive, AJCC 8th) gastric cancer and gastroesophageal junction adenocarcinoma will be enrolled. Patients will initially receive radiotherapy (95% planned target volume: 45 Gy/25 f) and concurrent chemotherapy (S-1: 40-60 mg twice a day) followed by six cycles of consolidated chemotherapy (SOX, consisting of S-1 and oxaliplatin) and surgery. The primary objective will assess pathological complete response; the secondary objectives will include toxicities assessing surgical complications, the tumor downstaging rate and the R0 resection rate.Investigation of total neoadjuvant therapy in gastric cancer is limited. The goal of this trial is to explore the efficacy and toxicity of total neoadjuvant therapy for locally advanced gastric cancer and gastroesophageal junction adenocarcinoma.Clinicaltrials.gov (NCT04062058, August 20, 2019).© 2022. The Author(s).