Objective: In this prospective, single blind-randomized study, we aimed to investigate the effect of controlled hypotension by esmolol vs. remifentanil on cerebral oxygen saturation (rSO2) by near-infrared spectroscopy (NIRS) in patients undergoing functional endoscopic sinus surgery (FESS). Material and Methods: One hundred fifty patients undergoing elective FESS under controlled hypotension were evaluated for study inclusion. Group allocation was performed in a randomized fashion. Controlled hypotension was provided using continuous remifentanil (Group R) or esmolol (Group E) infusion. rSO2 was assessed during controlled hypotension by NIRS monitoring. Demographic data, hemodynamic values, and rSO2 were recorded preoperatively, postinduction 5th min, intraoperatively (10,20,30,45,60,90 minutes), and 5 and 10 minutes after stopping hypotensive agents. The duration of surgery and anesthesia and surgeon satisfaction score were also recorded. Results: 126 patients were included in the study. Among the demographic data, only weight was found significantly different between the groups. The unfortunate fact is that there was no significant difference in the mean of minimum rSO2(p=0.186) and also in the median of the minimum mean arterial blood pressure (MAP) (p=0.312) between Group R and Group E. Surgeon satisfaction score was significantly higher in Group R (p<0.001). rSO2 (p<0.001, R2=0.67) was detected as the best predicting factor by the multiple regression model. While Heart rate (HR), MAP, and preinduction rSO2 added statistically significantly to the prediction(p<0.001), the type of hypotensive drug did not (p=0.979). Conclusion: Esmolol and remifentanil used for controlled hypotension did not cause significant rSO2 changes. Among the factors affecting rSO2 MAP, HR, and pre-induction rSO2 were detected, while the best predictor factor was pre-induction rSO2. Remifentanil provides a better surgical field than esmolol according to the VAS scale.