Objective To compare the effect of prophylactic infusion of norepinephrine (NE) and phenylephrine (PE) on cerebral oxygen saturation (ScO2) in the frontal lobe of parturients undergoing elective cesarean section under subarachnoid anaesthesia (SA), in order to identify a vasopressor that maintains ScO2 more stable. Methods A total of 106 parturients who underwent elective cesarean section under SA were included. According to the type of medication used, these participants were divided into two groups based on the random number table method: a PE group (group P, n=52) and an NE group (group N, n=54). An infusion pump was initiated simultaneously with subarachnoid administration. Both groups were infused over 30 min with PE at 50 µg/min and NE at 4 µg/min, respectively. Their general data (age, height, body weight, and body mass index) were recorded. The baseline values of ScO2, systolic blood pressure and heart rate were recorded, while the percentages of parturients in each group experiencing a decrease in ScO2 of ≥15% at 1, 3 min and 5 min after subarachnoid administration until fetal extraction were calculated. The incidences of intraoperative hypotension, bradycardia, nausea and vomiting, and dizziness, as well as the usage of rescue vasopressors (ephedrine and atropine) were recorded. Moreover, the time from subarachnoid administration to skin incision, the time rom skin incision to fetal extraction, and Apgar scores at 1 min and 5 min after neonatal extraction were documented. Results There were no statistical differences in general information between the two groups (all P>0.05). There were no statistical differences in the baseline values of systolic blood pressure, heart rate, and ScO2 between the two groups (all P>0.05). From subarachnoid administration to fetal extraction, no statistical differences were see in the percentage of parturients with ScO2 decreases of ≥15% at 1 min between the two groups (P>0.05), and group N showed significant lower percentages of parturients with ScO2 decreases of ≥15% at 3 min and 5 min than group P (all P<0.05). There were no statistical differences in the incidence of hypotension and the usage of ephedrine between the two groups (all P>0.05). However, group N presented statistical decreases in the incidences of dizziness, nausea and vomiting, bradycardia, and the usage of atropine, compared with group P (all P<0.05). There were no statistical differences in the time from subarachnoid administration to skin incision, the time from skin incision to fetal extraction, and Apgar scores at 1 min and 5 min after neonatal extraction between the two groups (all P>0.05). Conclusions NE and PE exhibit similar effects on preventing and treating maternal hypotension under SA, but NE is more favorable for maintaining stable heart rate and ScO2 during surgery. After NE administration, the incidences of dizziness and nausea and vomiting, and the usage of atropine during surgery are reduced.