To analyze whether acute kidney injury (AKI) patients diagnosed by elevated serum creatinine had a higher risk of in-hospital mortality following non-cardiac surgery compared with those diagnosed by oliguria alone according to Kidney Disease: Improving Global Outcomes (KDIGO) criteria. This was a secondary analysis of a previous retrospective cohort study. A total of 729 consecutive adult patients with high risk of AKI admitted to the intensive care unit (ICU) of Peking University First Hospital after non-cardiac surgery were enrolled in the previous study from July 2017 to June 2018. Postoperative AKI patients were diagnosed and categorized according to KDIGO criteria. In this secondary analysis, all patients with AKI were selected. Patients diagnosed by elevated serum creatinine were enrolled into the AKI-Scr group, while those with oliguria alone were included in the AKI-UO group. A multivariable logistic regression model was established to assess the relationship between elevated serum creatinine and in-hospital mortality in AKI patients. Of 188 AKI patients [(71±14) years, 114 males (60.6%)], 72 (38.3%) and 116 (61.7%) patients were enrolled in AKI-Scr and AKI-UO group, respectively. The rate of in-hospital mortality was 16.7% in AKI-Scr group, which was significantly higher than that in AKI-UO group (0.9%, <0.001). Furthermore, patients in AKI-Scr group had longer postoperative hospital and ICU stay, more duration of mechanical ventilation and higher total medical costs (all <0.05). Multivariate logistic regression analysis revealed that AKI-Scr (=20.286, 95%: 2.544-161.797, =0.004) and preoperative hypoproteinemia (=4.897, 95%: 1.240-19.329, =0.023) were independent risk factors for in-hospital mortality in postoperative AKI patients. AKI patients diagnosed by increased serum creatinine had a higher risk of in-hospital mortality following non-cardiac surgery, accompanied by several worsen short-term outcomes and higher total medical costs, compared with those diagnosed by oliguria alone according to the KDIGO criteria. More attention should be paid to AKI patients diagnosed by elevated serum creatinine, to improve the prognosis.