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High-level MET gene amplification is a rare but potentially actionable alteration in gastric cancer. Previous phase III trials of MET-targeted therapies enrolled broadly MET-positive populations without prospective selection for high-level MET amplification, and no MET-directed therapy is currently established for this disease. Here, we report a 74-year-old woman with heavily pretreated metastatic gastric adenocarcinoma harboring high-level MET amplification (copy number 21) identified by comprehensive genomic profiling. Following expert panel review, the patient received capmatinib through the BELIEVE trial (NCCH1901; jRCTs031190104) and achieved a confirmed partial response at 8 weeks, with a 43.7% reduction in the sum of target lesion diameters. The response was maintained at 16 weeks; disease progression was observed at 24 weeks, with a progression-free survival of approximately 5.5 months. In the context of a literature review of MET-targeted therapies in gastric cancer, this case supports further investigation of selective MET inhibition in gastric cancer with high-level MET amplification, a rare molecular subset not prospectively enriched in previous clinical trials.