Combination treatment with hypomethylating agents (HMAs) and venetoclax is being used increasingly in elderly patients with acute myeloid leukemia (AML). Venetoclax with HMAs has been reported to be associated with tumor lysis syndrome (TLS) in AML patients with high leukemic burden. We present a case of an elderly AML patient with low leukemic burden who developed TLS while receiving venetoclax and azacitidine (AZA). A 74-year-old man with newly diagnosed AML with NPM1 mutation received combination therapy with venetoclax and AZA in an outpatient clinic. Within 12 hours after starting venetoclax and AZA, the patient was admitted to the emergency room with fever, general weakness, and laboratory findings consistent with TLS. Based on our results, we recommend monitoring at the start of the treatment with venetoclax and HMAs to prevent and control TLS regardless of the leukemic burden and favorable genetic risk.