While precision medicine driven by genome sequencing has revolutionized cancer care,such as lung cancer,its impact on gastric cancer(GC)has been minimal.GC patients are routinely treated with chemotherapy,but only a fraction of them receive the clinical benefit.There is an urgent need to develop biomarkers or algorithms to select chemo-sensitive patients or apply targeted therapy.Here,we carried out retrospective analyses of 1,020 formalin-fixed,paraffin-embedded GC surgical resection samples from 5 hospitals and developed a mass spectrometry-based workflow for proteomic subtyping of GC.We identified two proteomic subtypes:the chemo-sensitive group(CSG)and the chemo-insensitive group(CIG)in the discovery set.The 5-year overall survival of CSG was significantly improved in patients who had received adjuvant chemotherapy after surgery compared with those who received surgery only(64.2％ vs.49.6％;Cox P-value=0.002),whereas no such improvement was observed in CIG(50.0％ vs.58.6％;Cox P-value=0.495).We validated these results in an independent validation set.Further,differential proteome analysis uncovered 9 FDA-approved drugs that may be applicable for targeted therapy of GC.A prospective study is warranted to test these findings for future GC patient care.