Objective A prospective randomized controlled trial was conducted to study the effectiveness and safety of intravenous different doses tranexamic acid (TXA) in single-level unilateral minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF). Methods The patients treated with single-level unilateral MIS-TLIF between September 2019 and October 2020 were enrolled and randomly classified into low-dose TXA (LD) group (n=39), high-dose TXA (HD) group (n=39), and placebo-controlled (PC) group (n=38). The LD, HD, and PC groups received intravenous TXA 20 mg/kg, TXA 50 mg/kg, the same volume of normal saline at 30 minute before skin incision after general anesthesia, respectively. There was no significant difference on baseline characteristics and preoperative laboratory results among 3 groups (P>0.05), including age, gender, body mass index, surgical segments, hematocrit (HCT), hemoglobin (HGB), prothrombin time (PT), international normalized ratio (INR), D-dimer, fibrin degradation products (FDP), activated partial prothromboplastin time (APTT), alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatinine (Cr), urea. The intraoperative blood loss (IBL), postoperative drainage volume, operation time, total blood loss (TBL), hidden blood loss (HBL), blood transfusion, hematological examination indexes on the first day after operation, and the incidence of complications within 1 month were compared among the 3 groups. Results There were 3, 2, and 4 patients in the LD, HD, and PC groups who underwent autologous blood transfusion, respectively, and there was no allogeneic blood transfusion patients in the 3 groups. There was no significant difference in IBL, postoperative drainage volume, and operation time between groups (P>0.05). The TBL, HBL, and the decreased value of HGB in LD and HD groups were significantly lower than those in PC group (P<0.05), and TBL and HBL in HD group were significantly lower than those in LD group (P<0.05); the decreased value of HGB between LD group and HD group showed no significant difference (P>0.05). On the first day after operation, D-dimer in LD and HD groups were significantly lower than that in PC group (P<0.05); there was no significant difference between LD and HD groups (P>0.05). There was no significant difference in other hematological indexes between groups (P>0.05). All patients were followed up 1 month, and there was no TXA-related complication such as deep venous thrombosis of lower extremity, pulmonary embolism, and epilepsy in the 3 groups. ConclusionIntravenous administration of TXA in single-level unilateral MIS-TLIF is effective and safe in reducing postoperative TBL and HBL within 1 day in a dose-dependent manner. Also, TXA can reduce postoperative fibrinolysis markers and do not increase the risk of thrombotic events, including deep venous thrombosis and pulmonary embolism.