The current study explored the efficacy of an intra-articular (IA) injection of allogeneic adipose tissue-derived stem cells (ADSCs) combined with xanthan gum (XG) in a rat osteoarthritis (OA) model. We confirmed that XG significantly inproved proliferation of ADSCs in a dose dependent manner in vitro. The rat OA model was induced by an anterior cruciate ligament transection (ACLT), and at 4 weeks after surgery, rats were divided into four groups: the XG-ADSCs group, the ADSCs group, the XG group and the phosphate-buffered saline (PBS) group. A single dose of 1 x 10(6) allogeneic ADSCs suspended in 1% XG, ADSCs suspended in PBS, 1% XG alone or PBS alone was injected into the OA joint of rats in the respective treatment groups. Rats were sacrificed at 8 weeks after surgery. Treatment outcomes were evaluated by weight-bearing control of the hind limbs, gross morphological analysis, histological analysis and specific staining of articular cartilage, and measurement of inflammatory factors in synovial fluid. For the rats in the XG-ADSC-s and ADSCs-treated groups, the weight-bearing percentage of the right hind limb was significantly increased compared to that in the PBS group and was sustained over 4 weeks. However, the positive effect in the XG-ADSCs group was significantly greater than that in the ADSCs group. For the rats in the XG group, the efficacy decreased during the third week after surgery. The articular cartilage was relatively normal in the XG-ADSCs group, and moderate degeneration was observed in the ADSCs and XG groups. ADSCs and XG-ADSC treatments significantly decreased the concentrations of IL-1 beta, TNF-alpha, MMP-3 and MMP-13 in synovial fluid; however, the attenuating effect of the XG-ADSCs treatment was significantly enhanced compared with that of the ADSCs treatment alone. These results indicate that a single IA injection of allogeneic ADSCs combined with XG efficiently attenuated OA progression with a therapeutic effect that was significantly greater than that of either ADSCs or XG alone. IA injection of XG-ADSCs might be an effective treatment for OA in humans. (C) 2017 Published by Elsevier Inc.