Hypertensive patients are more likely to experience latent cerebral ischemia causing regional cerebral oxygen saturation (rSO(2)) decrease during general anesthesia. The aim of this prospective observational study was to assess the incidence of decreased rSO(2) in hypertensive patients undergoing major abdominal surgery and the perioperative factors affecting this change in rSO(2). A total of 41 hypertensive patients were enrolled and stratified according to their hypertension as controlled and uncontrolled. The intraoperative rSO(2) and physiological data were routinely collected. The Mini-Mental State Exam (MMSE) was used to test cognitive function before surgery and after 4 days. Cerebral desaturation was defined as a decrease in rSO(2) of more than 20% of the baseline value. There were 20 patients (49%) suffering intraoperative cerebral desaturation classified into cerebral desaturation group (group D) and those 21 without intraoperative desaturation classified into normal group (group N). The area under the curve below 90 and 80% of baseline (AUC(rSO2 < 90% of baseline) and AUC(rSO2 < 80% of baseline)) was lower in patients of group N (2752.4 +/- 1453.3 min% and 0.0 min%) than in patients of group D (6264.9 +/- 1832.3 min% and 4486.5 +/- 1664.9 min%, P < 0.001). Comparing the two groups, the number of uncontrolled hypertensive individuals in group D (12/20) was significantly more than group N (4/21) (P = 0.007). A significant correlation was observed between relative decrease in MAP and relative decrease in rSO(2) (r(2) = 0.495, P < 0.001). Moreover, nine patients (45%) in group D occurred early postoperative cognitive function decline were more than three patients (14.3%) in group N (P = 0.031). This pilot study showed a large proportion of hypertensive patient experienced cerebral desaturation during major abdominal surgery and uncontrolled hypertension predisposed to this desaturation. NCT02147275 (registered at http://www.clinicaltrials.gov).