Background: Ketamine increases blood pressure and heart rate. Propofol is an anesthetic drug with rapid recovery, but it causes respiratory depression, low heart rate and low blood pressure. Combination of ketamine and propofol provides sedation, analgesia, and rapid recovery with hemodynamic stability and minimal respiratory depression. There have been a few studies about the effect of different concentrations of ketofol on amnesia in the children with leukemia undergoing intrathecal injection of chemotherapy drugs, so this study investigated the effect of two concentrations of ketofol (1/5 with midazolam and 1/10) on amnesia in these patients. Materials and Methods: This randomized, double blinded study was conducted on 64 ALL children aged between 5 to 12 years old and referred to Shahid Sadoughi hospital for intrathecal chemotherapy from July 2016 up to September 2016. The patients received titrated injection of a solution containing combination of one part of ketamine and ten parts of propofol (1: 10) (group I) or one part of ketamine and five parts of propofol (1: 5) with midazolam(0.5mg) (group II) to sedate at the fifth level of Ramsay Sedation Scale. Amnesia was evaluated using visual recognition of posters and recall of specific events. Drug side effects such as nausea, vomiting, hallucination, allergies, dizziness, cough, and apnea were also evaluated in the patients. Results: No significant difference between two groups was found regarding age and weight (p-value= 0.625, p-value= 0.830). Running Chi-square revealed no statistically different between groups in terms of posters recognition and recall of specific events. In terms of drug side effects, two groups were similar but for hallucination that was higher in group (p-value = 0.043). Conclusion: The results showed that ketofol 1/10 is superior in comparison to ketofol 1/5 with midazolam (0.5 mg) according to less side effects and similarity in amnesia induction.