Background and objectives Postcardiac surgery-associated acute kidney injury (AKI) is associated with up to 60% mortality rates of all cardiac surgery patients. This study aimed to study the renal-protective effect of dexmedetomidine in reducing the incidence of AKI following cardiac surgery. Patients and methods A total of 40 patients scheduled for cardiac surgery with cardiopulmonary bypass (CPB) were randomly allocated into two equal groups. In the study group, dexmedetomidine was given as an infusion of 0.4 μg/kg/h from induction of anesthesia till the end of surgery while in the control group, the patients received an equal volume of normal saline. The primary outcome of this study was the level of serum neutrophil gelatinase-associated lipocalin. The secondary outcomes were serum creatinine, hemodynamic parameters, operative time, aortic cross-clamp time, CPB time, and duration of ICU stay. Results Intraoperative and postoperative time variables and number of patients who developed hypotension were comparable between groups. Bradycardia developed more frequently in the dexmedetomidine group than in the placebo group. Serum neutrophil gelatinase-associated lipocalin after 2 h showed a statistically significant difference between groups. Serum creatinine showed no statistically significant difference between groups. Conclusion Dexmedetomidine could have a protective role in renal function during cardiac surgery using the CPB.