Objective To investigate whether there is a dose-dependent positive effect of dexmedetomidine on neutrophil gelatinase-associated lipocalin (NGAL) and renal function in elderly patients after valve replacement. Methods The patients, aged >60 years, who underwent valve replacement in our hospital from March 2016 to May 2017 and met the inclusion criteria were enrolled. A total of 92 consecutively admitted patients who met the inclusion criteria were randomly divided into placebo group, middle-dose group, and high-dose group. The patients in the placebo group were given normal saline, and those in the middle- and high-dose groups were given a loading dose of dexmedetomidine of 0.5 μg/kg and 1.0 μg/kg, respectively, followed by infusion at the same maintenance dose. The infusion rate was adjusted to achieve the sedative effect with a Ramsey sedation score of 2 or 3. Serum samples were collected before surgery and at 24 and 48 hours after surgery to measure serum NGAL and renal function (serum creatinine [SCr], blood urea nitrogen [BUN], and estimated glomerular filtration rate). Results There were no significant differences between the three groups in baseline data, surgical risk, perioperative conditions, and perioperative renal function, and there were also no significant differences between the three groups in the mean values of renal function parameters (BUN, SCr, and creatinine clearance rate) (P>0.05). There was no significant difference in serum NGAL between the three groups before surgery (P=0.410). At 24 hours after surgery, the level of NGAL was 178.4±72.5 ng/ml in the placebo group, 102±68.4 ng/ml in the middle-dose group, and 68.5±47.7 ng/ml in the high-dose group (P<0.001). At 48 hours after surgery, there was no significant difference in NGAL between the middle-dose group and the high-dose group (P=0.066), but both groups had significantly lower NGAL than the placebo group. Conclusion For elderly patients after valve replacement, dexmedetomidine infusion can prevent postoperative renal injury and protect renal function in a dose-dependent manner. Measurement of blood NGAL helps to identify the change in renal function in the early stage.