Abstract: Objective To investigate the pathologic effect of intra-articular injection of ozone on the ar-ticular cartilage, and to explore the feasibility of direct intra-articular injection of ozone in the treatment of arthri-tis. Methods Animals with induced-arthritis were given three different concentrations of medical ozone (high and low concentrations)by intra-articular injection, to observe pathological changes of cartilage. Results The score result of cartilage degradation was based on Mankin's grading scale,and the higher the score,the severer the symptom was. The score of normal articular cartilage was 0.0±0.0, and the score of model group was sig-nificantly higher than that of the normal group(P<0.01), while obviously lower than that of the treatment group (P<0.01). Moreover,the score of high-dose treatment group was significantly higher than that of low-dose group(P<0.01). Conclusion Long-term intra-articular injection of ozone had a bad effect on articular carti-lage, and damage-level was increased with the enhancement of ozone concentrations.