Objective To observe the relationship of pre-operative serum brain natriuretic peptide (BNP) with risk of acute kidney injury (AKI) after cardiac surgery. Methods We collected 182 patients undergoing cardiac surgery at Department of Cardiac Surgery, Changhai Hospital from Jan. 2012 to Jan. 2013. The surgical procedures included coronary artery bypass graft (CABG),valve replacement, and combined surgery (CABG+valve replacement). According to the preoperative BNP levels, the patients were divided into five groups in an ascending order. The definition and classification weres accorded to the latest AKI KDIGO (Kidney Disease: Improving Global Outcomes) guideline; the AKI incidence was obtained from patients with different BNP levels. Receiver operating characteristic (ROC) curves were used to evaluate the value of BNP level as a predictor of AKI. Results The average age of the 182 patients was (68.6±8.9) years old, with male being 65.9% (120/182). The surgery procedures including 82 CABG (45.0%),57 valve replacement (31.3%), and 43 combined surgery (CABG valve replacement) (23.6%). We found that age, basic renal function and pre-operative BNP levels were significantly different between the five BNP groups (P<0.05). The incidence of AKI was 33.5% (61/182) in this study. The incidence rates of stage 1 AKI and total AKI significantly increased with increase of BNP levels in the five BNP groups (P<0.05). As a predictor of AKI ROC curves, BNP area under the curve (AUC) was 0.687 (95% CI: 0.607-0.768). Conclusion Pre-operative BNP level is associated with post-operative AKI in high risk patients undergoing cardiac surgery, and it is a potential predictor of AKI risk stratification after cardiac surgery.