Objective To analyze the prognosis of the elderly patients with acute kidney injury (AKI) and those suffering from acute on chronic kidney injury. Methods A total of 147 patients (105 males and 42 females, at a mean age of 83.95±7.04) with acute on chronic AKI (AonC) and 270 cases (226 males and 44 females, at a mean age of 81.75±6.98) with denovo AKI admitted in our center from August 2009 to October 2013 were enrolled in this study. Their short-term outcomes (within 1 year) were analyzed. Results The 30-day mortality was significantly higher in the AKI than the AonC patients (P<0.05), but there were no differences in that of 90-day and 1-year (P>0.05). No difference was seen in the recovery of renal function between the survivals from the 2 group (P>0.05). There were no differences in the 30-day,90-day,1-year mortalities among the AonC patients with different estimated glomerular filtration rates (eGFR). COX multivariate regression analysis showed that complication with chronic kidney disease (CKD) had no relation with the 30-day mortality (P=0.068), but is associated with AKI stage, anemia,hypoalbuminemia,heart failure, cancer, and multiple organ dysfunction syndrome (MODS). Renal replacement therapy was the protective factor for AonC patients. Conclusion The incidence and mortality of AKI were quite high in the AKI elderly patients.Complication of CKD is not related with their short-term prognosis.