Objective To evaluate the efficacy and safety of a subanesthetic dose of esketamine in preventing postoperative nausea and vomiting following carboprost administration during cesarean section. Methods One hundred thirty?five full?term singleton parturients， ASAⅠ-Ⅱ， aged 20 - 40 years， scheduled for elective cesarean section， were recruited. They were randomly assigned to three groups （n = 45）： the normal saline group （Group C）， the palonosetron group （Group P）， and the esketamine group （Group E）. All parturients received combined spinal?epidural anesthesia， achieving a sensory level of T_5?7. Following umbilical cord clamping， carboprost tromethamine was injected into the uterine body. Concurrently， Group C received intravenous normal saline， Group P received palonosetron， and Group E received esketamine. The incidence of nausea， vomiting， and chest discomfort was recorded from the time of carboprost administration until the parturients left the operating theater. Additionally， mean arterial pressure （MAP）， heart rate （HR）， oxygen saturation （SpO₂）， and Ramsay sedation scores were measured at six time points： upon entering the room （T₀）， 1 minute before intervention （T₁）， 2 minutes （T₂）， 5 minutes （T₃）， 15 minutes （T₄）， and 30 minutes （T5） post?intervention. Maternal satisfaction was evaluated as the parturients left the operating room. Results Compared with group C， the incidence of nausea， vomiting， and chest discomfort in group E was significantly lower （all P < 0.05）. Additionally， group E showed a significantly lower incidence of nausea and chest discomfort compared to group P （all P < 0.05）. In terms of maternal satisfaction， group E reported significantly higher levels than both group C （P < 0.05） and group P （P < 0.05）. No significant differences were observed in the incidence of nausea， vomiting， chest discomfort， or satisfaction between the other groups （P > 0.05）. Conclusion The administration of subanesthetic doses of esketamine significantly decreases the incidence of adverse effects such as nausea， vomiting， and chest tightness that are commonly associated with carboprost tromethamine use during cesarean sections， thereby enhancing patient satisfaction in the perioperative period.