Abstract Background Postoperative pain is common in pediatric urological surgery. The study assess the impact of perioperative intravenous infusion of low-dose esketamine on postoperative pain in pediatric urological surgery. Methods Pediatric patients (n = 80) undergoing urological surgery were randomized into four groups. Patients in the control group were administered an analgesic pump containing only hydromorphone at a dose of 0.1 mg/kg (Hydromorphone Group 1, H1) or 0.15 mg/kg (Hydromorphone Group 2, H2). Patients in the experimental group were injected intravenously with 0.3 mg/kg of esketamine (Esketamine group 1, ES1) or equal volume of saline (Esketamine Group 2, ES2) during anesthesia induction. Esketamine 1.0 mg/kg and hydromorphone 0.1 mg/kg were added to the analgesic pump. Face, Leg, Activity, Crying, and Comfort (FLACC) scale or the Numerical Rating Scale (NRS) and adverse effects were recorded at 2, 6, 24, and 48 h postoperatively. Additionally, total and effective PCA button presses were recorded. Results In comparison to the H1 group, the pain scores were notably reduced at all postoperative time points in both the ES1 and H2 groups. The ES2 group exhibited lower pain scores only at 24 and 48 h postoperatively. When compared to the H2 group, there were no significant differences in pain scores at various postoperative time points in the ES2 group. However, the ES1 group demonstrated significantly lower pain scores at 6, 24 and 48 h postoperatively, and these scores were also significantly lower than those observed in the ES2 group. The total and effective number of PCA button presses in the ES1, ES2 and H2 group were lower than that in the H1 group (P