Neoadjuvant chemotherapy has been a recent focus in the treatment for advanced gastric cancer. Although the preoperative chemotherapeutic regimen of S-1 and CDDP is regarded as effective, safe and well tolerable according to previous clinical study, we experienced a 74-year-old woman who suffered from life-threatening adverse events including severe myelosuppression during the neoadjuvant chemotherapy. Although the patient did not experience any severe adverse events during the first course of treatment, on day 18 of the second course of chemotherapy, she was hospitalized because of anorexia and severe dehydration, leading to following grade 4 leukopenia/neutropenia, bacteremia, and disseminated intravascular coagulation (DIC). She finally recovered from the life-threatening adverse events with intensive therapy and eventually had a distal gastrectomy. Clinicians need to be alert especially to renal dysfunction that induces severe myelosuppression during chemotherapy with S-1, which contains 5-chloro-2,4-dihydroxypyridine (CDHP), a renal excretory inhibitor of dihydropyrimidine dehydrogenase (DPD).