Background: Use of Local anaesthetics for caudal block in children may be associated with limited duration of action, systemic toxicity and motor block. This may be mitigated with use of a low dose of S-ketamine which has good analgesic effect in the caudal route. Objective: To compare the analgesic efficacy of bupivacaine and preservative free S (+)- ketamine when used for caudal block in children. Methods: Seventy, six children aged 2-7 years of ASA class I or II scheduled for inguinal herniorrhaphy were recruited into this prospective double blinded study. They were randomly allocated into two groups B and K of thirty, eight each. Children in Group B received caudal Bupivacaine 0.25% (1ml/kg) while those in Group K received caudal S –Ketamine 1mg/kg. The outcomes assessed included duration of analgesia, mean pain scores, mean time to ambulation in the post-operative period and incidence of side effects such as sedation, shivering and vomiting. Results: The mean duration of analgesia was significantly prolonged in the ketamine group compared to the bupivacaine group (p=0.0000). Mean post-operative pain score was comparable between bupivacaine and ketamine groups. Average Sedation score was not significantly different between the two groups. The mean time to first ambulation without support was significantly shorter in the ketamine group than in the bupivacaine group (p=0.001). Conclusion: Caudal S (+) ketamine (1mg/kg) is superior to (0.25%) bupivacaine 1ml/kg in the duration of analgesia for herniorrhaphy in children.