Objective To investigate the value of arthroscope in the diagnosis and treatment of knee synovitis. Methods 50 cases of knee synovitis diagnosed by arthroscopy and treated by endoscopic synovectomy were studied. There were 10 cases with rheumatoid arthritis, 11 cases with pigmented villonodular synovitis,5 cases with chronic infection of knee joint,12 cases with chronic non-specific synovitis,5 ca-ses with tuberculous synovitis of the knee,4 cases with meniscus injury,3 cases with unknown cause. The efficacy of the treatment was recor-ded. Results All these cases were clearly diagnosed by microscopic examination combined with synovial pathological examination,and 10 cases were corrected with clinical diagnosis post-operation. All cases received primary healing without serious complications. All cases were followed up,and 6 cases of pigmented villonodular synovitis,2 cases of rheumatoid arthritis,1 case of chronic non-specific synovitis and 1 case of tuberculous synovitis of the knee had recurred. The total effective rate was 80. 0%. Conclusion The application of arthroscopy and syno-vial biopsy was effective in diagnosis. Arthroscopic synovectomy had good effect on treatment with less trauma and complications.