Studies have linked Accountable Care Organizations (ACOs) to improved primary care, but there is little research on how ACOs affect care in other settings. We examined whether Medicare ACOs have improved hospital quality of care, specifically focusing on preventable inpatient mortality. We used 2008-2014 Healthcare Cost and Utilization Project hospital discharge data from 34 states’ Medicare ACO and non-ACO hospitals in conjunction with data from the American Hospital Association Annual Survey and the Survey of Care Systems and Payment. We estimated discharge-level logistic regression models that measured the relationship between ACO affiliation and mortality following admissions for acute myocardial infarction, abdominal aortic aneurysm (AAA) repair, coronary artery bypass grafting, and pneumonia, controlling for patient demographic mix, hospital, and year. Our results suggest that, on average, Medicare ACO hospitals are not associated with improved mortality rates for the studied IQI conditions. Stakeholders may potentially consider providing ACOs with incentives or designing new programs for ACOs to target inpatient mortality reductions.