Objective To determine the median effective dose (ED₅₀) of remimazolam for preoperative sedation in pediatric patients aged 1-6 years using the modified Dixon sequential method. Methods This is a prospective clinical study. Pediatric patients scheduled for elective short surgery (surgery time ≤1 h) under general anesthesia from January to July 2023 were selected. Inclusion criteria were age 1-6 years, an ASA physical status Ⅰ-Ⅱ and the preoperative parent separation anxiety scale (PSAS) score ≥3 points. Remimazolam was administered intravenously preoperatively, and its sedative effect was assessed. The modified Dixon sequential method was used to determine the ED₅₀ of remimazolam, with the initial dose set at 0.10 mg/kg and the dose increment set at 0.02 mg/kg. Sedation was considered successful (positive, included in positive group) if the child with sedation score ≥2 points, preoperative PSAS score <3 points,and the mask acceptance score of 4 points during anesthesia induction. If any criterion was not met, sedation was considered failure (negative, included in negative group), and the next patient's dosage was increased by 0.02 mg/kg based on the previous patient's dosage. The test was completed after 7 consecutive positive and negative turning points appeared alternately. Probabilistic unit regression analysis was used to determine the ED₅₀, ED₉₅ and the corresponding 95% confidence interval (CI) of remimazolam for preoperative sedation. Postoperative recovery time and adverse events such as airway spasm, respiratory depression, hypotension, nausea and vomiting during anesthesia were recorded. Results A total of 23 pediatric patients were included, with 13 in positive group and 10 in negative group. There were no statistically significant differences in mean arterial pressure, pulse oxygen saturation or heart rate before and after sedation (P>0.05). Compared with negative group, positive group showed a significant reduction in preoperative parent separation anxiety and an increase in mask acceptance during anesthesia (P<0.05). There was no significant difference in sedation score and anesthesia awakening time between two groups (P>0.05). The ED₅₀ of remimazolam for preoperative sedation in pediatric patients aged 1-6 years was 0.051 mg/kg (95%CI 0.033-0.065 mg/kg), and the ED₉₅ was 0.077 mg/kg (95%CI 0.064-0.161 mg/kg). No adverse events such as airway spasm, respiratory depression, hypotension, nausea and vomiting occurred during anesthesia in any of pediatric patients. Conclusion The ED₅₀ of intravenous administration of remimazolam for preoperative sedation in pediatric patients aged 1-6 years is 0.051 mg/kg (95%CI 0.033-0.065 mg/kg).