We assessed whether the admission fasting plasma glucose (FPG) levels were associated with all-cause mortality and left ventricular (LV) function in older patients with acute myocardial infarction (AMI). A total of 1854 consecutive patients were categorized into 4 groups: hypoglycemia, euglycemia, mild hyperglycemia, and severe hyperglycemia. The primary outcomes were in-hospital/3-year mortality and LV function. There was a near-linear relationship between FPG and Killip class. However, no significant correlation was found between FPG levels and LV ejection fraction. Both FPG levels and Killip classes were all independent significant predictors of mortality. Compared with the euglycemia group, both the hypo-and hyperglycemia groups were associated with higher in-hospital and 3-year mortality. In older patients with AMI, the FPG values had differential influences on LV function and mortality. There was a U-shaped relationship between FPG and in-hospital/3-year mortality, and a near-linear relationship between increased admission glucose levels and higher Killip classification.