Objectives: The study was conducted to compare the combined effect of dexmedetomidine (DEX) and oral or suppository Yokukansan (YKS) on sedation after cardiac surgery in pediatric patients. Methods: Eighteen postoperative patients were divided into three groups according to YKS combined with continued administration of DEX: non-YKS (NY) group, gastric tube (oral) YKS (GY) group, and intrarectal suppository YKS (RY) group. YKS was administered at a dose of 0.1 g/kg every four hours. The sedation level was evaluated using Richmond Agitation-Sedation Scale and Behavioural Observational Pain Scale, and ketamine was administered for patients with scores ≥2 in either scales. The total dose of ketamine administered per body weight was used to define the sedative effect. Results: The ketamine dose (median) was 1.5, 1.0, and 0 mg/kg/day in NY, GY, and RY groups, respectively. Compared with the NY group, the GY group used less ketamine but the difference was not significant (P=0.49) and the RY group used a significantly lower dose (P=0.03). Conclusions: The combination of DEX and suppository YKS was effective for sedation in children after cardiac surgery, while DEX combined with gastric tube (oral) YKS was not sufficient in efficacy.