Venetoclax with azacitidine (ven/aza) has emerged as a promising treatment regimen for acute myeloid leukemia (AML), with a high percentage of clinical remissions in newly diagnosed patients. However, approximately 30% of newly diagnosed patients and the majority of patients who have relapsed do not achieve remission with ven/aza. We previously reported that ven/aza efficacy is based on eradication of AML stem cells through a mechanism involving inhibition of amino acid metabolism, a process required in primitive AML cells to drive oxidative phosphorylation. Herein we demonstrate that resistance to ven/aza occurs via upregulation of fatty acid oxidation (FAO), which occurs either due to RAS pathway mutations or as a compensatory adaptation in relapsed disease. Utilization of FAO obviates the need for amino acid metabolism, thereby rendering ven/aza ineffective. Pharmacological inhibition of FAO restores sensitivity to ven/aza in drug-resistant AML cells. We propose inhibition of FAO as a therapeutic strategy to address ven/aza resistance.