The purpose of this meta-analysis was to investigate the efficacy and safety of mesenchymal stem cells (MSCs) combined with platelet-rich plasma (PRP) in the treatment of knee osteoarthritis (KOA).Systematic review and meta-analysis.Patients with KOA.Use of MSCs+PRP.Visual Analogue Scale (VAS) score, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, Knee Injury and Osteoarthritis Outcome Score (KOOS) and adverse reactions.PubMed, Cochrane Library, Embase and China National Knowledge Infrastructure were searched from inception to 15 July 2021.The OR or weighted mean difference (WMD) of relevant outcome indicators was calculated. Study quality was evaluated using the risk-of-bias assessment tool version 2.0. Heterogeneity among studies was evaluated by calculating I2. If I2＜50%, a fixed-effect model was applied; conversely, if I2 ≥50%, a random-effect model was applied.Six controlled clinical trials with 493 cases were included. The meta-analysis results showed that in terms of the VAS score 3 months after treatment, MSCs+PRP had no significant effect on the reduction of the VAS score in patients with KOA compared with the control (p=0.09), hyaluronic acid (HA) (p=0.15) or PRP alone (p=0.07). MSCs+PRP was more effective in reducing the VAS score at 6 and 12 months after treatment than the control (WMD=-0.55, 95% CI -0.87 to -0.22, p<0.001), HA (WMD=-1.20, 95% CI -2.28 to -0.13, p=0.03) or PRP alone (WMD=-0.54, 95% CI -0.89 to -0.18, p=0.003). Regarding the decrease in the total WOMAC score at 3 and 6 months after treatment, MSCs+PRP showed better clinical efficacy than the control or HA alone (p<0.01). Compared with the control, MSCs+PRP exhibited no significant difference in reducing the total WOMAC score 12 months after treatment (p=0.39). There was no significant difference between MSCs+PRP and the control in terms of improvement of the KOOS 12 months after treatment (p=0.16). Compared with MSCs alone, MSCs+PRP exhibited no significant difference in the incidence of adverse reactions (p=0.22) 12 months after treatment.Treatment with MSCs+PRP showed good clinical efficacy in improving pain and joint function in patients with KOA. Compared with MSCs alone, there was no significant difference in the incidence of adverse reactions with MSCs+PRP.CRD 42021275830.© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.