Background and aim: The study aim was to compare whether high dose or low dose tranexamic acid have an effect in decreasing perioperative blood loss in spine surgery case and determine whether the expected reduction in the bleeding was capable of reducing the need for blood transfusion. Patients and methods: This study was prospective, double blind, RCT study in which sixty patients were scheduled for posterior arthrodesis of spinal cord with fusion of one or two levels under general anesthesia. The patients were randomly allocated into three equal groups. Group C (control) received normal saline, group HD (high does) received 50 mg/ kg of tranexamic acid administered over 30 min before skin incision and continued at the rate of 20 mg/kg/h until the end of the procedure and group LD (low does) received 10 mg/ kg of tranexamic acid over 30 min before skin incision and continued at the rate of 1 mg/ kg/h until the end of the procedure. The total amount of blood loss intraoperative and in the first 24 hours postoperative and hemoglobin concentration (preoperative and one day postoperative) were recorded. Results: HD group and LD group showed a highly significant decrease in blood loss in comparison with the control group (p