32 patients with Kellgren-Lawrence grade II-IV knee osteoarthritis were randomized to one of three injection groups: high-dose autologous bone marrow-derived mesenchymal stem cell injection and hyaluronic acid injection (high-dose MSC group), low-dose autologous bone marrow-derived mesenchymal stem cell injection and hyaluronic acid injection (low-dose MSC group), or hyaluronic acid injection alone (control group). Patients were assessed for safety and efficacy outcomes over 3, 6, and 12 month follow-up in this phase I/II study. Safety analysis reported no serious treatment-related adverse events in any group. Efficacy results demonstrated significant within-group improvement after 12 months in the high-dose MSC group for VAS pain, WOMAC pain, WOMAC stiffness, and WOMAC function, whereas within-group improvement in the low-dose MSC group was only noted for WOMAC stiffness after 6 and 12 months, and within-group improvement in the control group was only noted for WOMAC function at 3 and 6 months. Knee range of motion was significantly improved from baseline in the high-dose MSC group after 3, 6 and 12 months, and in the low-dose MSC group after 12 months; no significant change in knee range of motion was noted in the control group.