Objective To evaluate the clinical efficacy and safety of intra-articular injection of human umbilical cord blood mesenchymal stem cells (hUC-MSCs) for knee osteoarthritis.Methods A total of 66 patients with knee osteoarthritis were enrolled between January 2024 and January 2025 and randomly divided into a control group and an observation group using a random number table method, with 33 patients in each group. The control group received intra-articular sodium hyaluronate injection, while the observation group received intra-articular hUC-MSCs injection. All patients completed 12 months of follow-up. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Lequesne index, and Lysholm knee scores were compared before treatment, and at 3, 6, and 12 months after treatment. Adverse events including joint pain, swelling, and effusion were recorded.Results At 3, 6, and 12 months after treatment, WOMAC and Lequesne scores showed a decreasing trend in both groups, while Lysholm scores showed an increasing trend. The improvement in the above scores was significantly better in the observation group than in the control group at all time points (all P < 0.05). There was no significant difference in the overall incidence of adverse reactions between the two groups (P > 0.05). All adverse reactions were relieved after symptomatic treatment with non-steroidal anti-inflammatory drugs, and no serious adverse events occurred.Conclusion Intra-articular injection of hUC-MSCs effectively improves knee function, relieves pain, and reduces inflammation in patients with knee osteoarthritis. The treatment demonstrates good safety with manageable adverse events and substantial clinical application value.