BackgroundKetamine is administered in the perioperative period for its benefits in analgesia, anti-agitation and anti-depression when administered at a small dose. However, it is not clear whether the intra-operative administration of ketamine would affect emergence under sevoflurane anesthesia. To investigate this effect, we designed this trial.MethodsIn this randomized, double-blind, placebo-controlled study, we enrolled 44 female patients aged 18–60 who were scheduled to elective laparoscopic gynecological surgeries. All patients were randomly assigned to saline or s-ketamine group. In s-ketamine group, patients received 0.125 mg/kg s-ketamine 30 min after the start of surgery. In saline group, patients were administered the same volume of saline. Sevoflurane and remifentanil were used to maintain general anesthesia. The primary outcome was emergence time. We also assessed postoperative agitation, cognitive function, and delirium. In addition, we collected and analyzed prefrontal electroencephalogram (EEG) during and after general anesthesia.ResultsThere were no significant differences in emergence time between s-ketamine group and saline group (10.80 ± 3.77 min vs. 10.00 ± 2.78 min,P= 0.457). Neither postoperative agitation (4 [3, 4] vs. 4 [3, 4],P= 0.835) nor cognitive function (25.84 ± 2.69 vs. 25.55 ± 2.19,P= 0.412) differed between groups. No postoperative delirium was observed in either group. Subanesthetic s-ketamine resulted in active EEG with decreased power of slow (-0.35 ± 1.13 dB vs. -1.63 ± 1.03 dB,P= 0.003), delta (-0.22 ± 1.11 dB vs. -1.32 ± 1.09 dB,P= 0.011) and alpha (-0.31 ± 0.71 dB vs. -1.71 ± 1.34 dB,P= 0.0003) waves and increased power of beta-gamma bands (-0.30 ± 0.89 dB vs. 4.20 ± 2.08 dB,P< 0.0001) during sevoflurane anesthesia, as well as an increased alpha peak frequency (-0.16 ± 0.48 Hz vs. 0.31 ± 0.73 Hz,P= 0.026). EEG patterns did not differ during the recovery period after emergence between groups.ConclusionKetamine administered during sevoflurane anesthesia had no apparent influence on emergence time in young and middle-aged female patients undergoing laparoscopic surgery. Subanesthetic s-ketamine induced an active prefrontal EEG pattern during sevoflurane anesthesia but did not raise neurological side effects after surgery.Trial registrationChinese Clinical Trial Registry, ChiCTR2100046479 (date: 16/05/2021).Supplementary InformationThe online version contains supplementary material available at 10.1186/s12871-023-02170-5.