BACKGROUND: Hemarthrosis after anterior cruciate ligament (ACL) reconstruction can create many adverse joint effects. Tranexamic acid (TXA) can be used to minimize hemarthrosis and associated pain after ACL reconstruction. We aimed to compare the efficacies of intravenous (IV) administration and intra-articular (IA) injection of TXA during ACL reconstruction for reducing postoperative hemarthrosis. METHODS: A total of 120 patients who underwent arthroscopic ACL reconstruction were included in this prospective and randomized study. All patients were randomized into three groups: IV group, IA group and placebo group. Patients in the IV group received intravenously administered TXA (15 mg/kg in 100 mL of saline solution) 10 min before tourniquet release; patients in the IA group received intra-articular TXA (15 mg/kg in 100 mL of saline solution) injected via the drainage tube; and patients in the placebo group received an equivalent volume of normal saline administered into the knee joint cavity and intravenously. Drainage tubes were removed 24 h after surgery, and all enrolled patients experienced a 4-week follow-up period. The drain output volume, visual analogue scale (VAS) score, patellar circumference, hemarthrosis grade and Lysholm score of all patients were recorded. RESULTS: Both the IV group and the IA group had significantly lower drain output volumes at day 1, lower VAS scores at weeks 1 and 2, smaller patellar circumferences at weeks 1 and 2, and lower hemarthrosis grades at weeks 1 and 2 than the placebo group (p < 0.05). There were no significant differences in drain output volume, VAS score, patellar circumference or hemarthrosis grade between the IV group and the IA group at any time point (p > 0.05). No obvious differences in Lysholm score were observed between any pair of groups at week 4 (p > 0.05)). Neither infection nor deep vein thrombosis occurred in any group. CONCLUSIONS: Both intravenous administration and intra-articular injection can reduce intra-articular hemarthrosis, joint pain and swelling during ACL reconstruction. No significant difference in the efficacies of reducing hemarthrosis, joint pain and swelling was found between intravenous administration and intra-articular injection. TRIAL REGISTRATION: The study was registered by the Chinese Clinical Trial Registry (The comparative efficacies of intravenous administration and intra-articular injection of tranexamic acid during anterior cruciate ligament reconstruction; ChiCTR-INR-17012217 ; August 1, 2017).