Objective To explore the feasibility and efficiency of bispectral index (BIS) monitor for assessing the sedation level of mechanically ventilated patients in the Pediatric Intensive Care Unit (PICU). Methods A total of 19 patients who underwent mechanical ventilation were selected. Patients were intravenously injected with midazolam 5-15 min after mechanical ventilation until the BIS score reached 60-80. Then after 30, 60, and 120 min, the concentration of oxygen inhalation (FiO2), transcutaneous oxygen saturation (SpO2), and values and scores of BIS, sedation-agitation scale (SAS), and Ramsay sedation scale (RSS) were recorded. The correlation of three sedation scales was analyzed. Results All patients were sedated. After being sedated, FiO2 of patients significantly decreased and SpO2 significantly increased (P<0.05). BIS value was significantly correlated with subjective scores. BIS value was significantly and negatively correlated with RSS scores (r=-0.650，P<0.05) and significantly and positively correlated with SAS scores (r=0.626，P<0.05). Conclusion BIS monitor is a simple and efficient method to assess the sedation level of mechanically ventilated patients and an ideal objective index for assessing the sedation level of mechanically ventilated patients in ICU.