S (+) ketamine has more potent analgesic effects and less psychomimetic side effects than rasemic ketamine. The aim of this study was to compare the hemodynamic and sedative effects of S (+) ketamine in rectal route in two different doses. Forty children, of 2-10 years old, ASA physical status I and II, were randomly assigned to two groups. In Group I (n=21), a combination of 3 mgkg-1 S (+) ketamine and 0.02 mgkg-1 atropine in 0.5 mLkg-1 volume was administe-red by rectal route. In Group II (n=19) 6 mgkg-1 S (+) ketamine and 0.02 mgkg-1 atropine was administered in the same way. Control heart rate, systolic and diastolic blood pressure, oxygen saturation, respiratory rate, sedation and anxiety scores recorded just before and after rectal premedication in every 10 minutes since the inductions of anesthesia. Tolerance to face mask during anesthesia was graded by scoring system and the reactions to IV cannulation were recorded. Sevoflurane, nitrous oxide and oxygen had been used for induction and maintenance of anesthesia. We used atracurium for muscle relaxation. In recovery period, heart rate, systolic and diastolic blood pressure, oxygen saturation, respiratory rate had been recorded with consciousness scores and agitation scores for every 5 minutes. There was no comparable difference in hemodynamic parameters after the premedication and during the recovery period between groups (p>0.05). Eight children exerted a reaction to rectal application by crying. In Group II face mask acceptance was better and reaction to intravenous cannulation was lesser than Group I (p<0.05). In recovery period, there was no difference between group in consciousness and agitation scores. In conclusion, rectal S (+) ketamine premedication in doses of 3 mgkg-1 and 6 mgkg-1 exerted a good sedation level, but 6 mgkg-1 produced a good mask acceptance and intravenous cannulation tolerance without hemodynamic changes.