Objectives: After emphasis on prevention and early recognition of acute kidney injury (AKI) from the KDIGO 2012 AKI guideline, in-hospital AKI occurrence had reduced during the past two decades. However, understanding the time trend of post-operative AKI (PO-AKI) is lacking yet. Methods: A retrospective cohort study was performed at three referral hospitals from 2005 to 2020. The patients who underwent non-cardiac major surgery having more than 1 hour of operation time at 5 departments including general surgery, gynecology, urology, neurosurgery, and orthopedic surgery were enrolled. PO-AKI was defined as KDIGO AKI criteria within 7 days after surgery. Severe PO-AKI (S-PO-AKI) was defined as stage 2 or 3 AKI. The time period was divided into 3-year intervals and evaluated by join-point regression analysis and multivariate logistic regression. Results: A total of 171,273 patients were included. During the study period, 9,035 (5.3%) PO-AKI and 1243 (0.7%) S-PO-AKI occurred. The patients were older and more women. They had more comorbidities including diabetes mellitus (5.6% → 15.7%), hypertension (12.4% → 31.5%), coronary artery disease (1.9% → 4.4%) as times go by. Surgery duration tended to be reduced recently. Preoperative nonsteroidal anti-inflammatory drug usage was decreased whereas diuretics and renin-angiotensin-aldosterone system blockades uses were increased with time. The PO-AKI incidence had decreased from 8.9 % in 2014 to 4.6% in 2020. In join-point analysis, PO-AKI incidence decreased with annual percent change (APC) of -4.9 % per year (95% confidence interval [CI] -6.2% – -3.5%, p-value <0.001), Although, S-PO-AKI was not (APC -0.3%, 95% CI -2.1 – 1.5%, p-value = 0.732, Figure 1). These trends were remained similarly after adjustment with age, sex, co-morbidities, blood pressure, serum albumin, serum sodium, dipstick albuminuria, and perioperative nephrotoxic drugs. Conclusions: In this large-scale study, we found the PO-AKI had decreased recently, although the incidence of S-PO-AKI still had not changed.