Objectives: To investigate the applied value of synovial biopsy with Parker-Pearson needle and its affecting factors.Methods: 295 patients with arthropathies or systemic diseases with knees involved have received synovial biopsies in knees by Parker-Pearson needle.Total area of qualified synovial membrane was measured and histological Krenns synovitis score was assessed according to H&E staining under microscope.Effective biopsy was defined as obtaining qualified synovium with intact lining and sublining layers.High effective biopsy was defined as obtaining at least three pieces of qualified synovium and their total area ≥2.5 mm2.Results:① 322 cases of synovial biopsies were performed.The rate of effective biopsy was 85% and the rate of high effective biopsy was 63%.In effective biopsies, the median of the total area of qualified synovium was 5.3mm2,and the median pieces of qualified synovium were five.② For 25 cases of repeat synovial biopsies, the rate of effective biopsy was 84%.③ For five cases, urate crystal in synovium was confirmed under polarizing microscope, supporting their diagnosis as gout.One patient with pain and swelling in one knee and one ankle was diagnosed as oxalate crystal induced arthritis, due to calcium oxalate crystal found in synovium.Another patient with chronic pain and swelling in one knee was diagnosed as tuberculous synovitis, due to his strongly positive PPD test and tuberculoid nodules formation and necrotic tissue found in synovium, although several detections of acid-fast bacilli in synovial fluid were negative and culture of tubercle bacillus in synovial fluid was also negative.For a young girl with swelling but no pain in one knee, hemosiderin and multinucleated giant cells were found in her synovium, suggesting the diagnosis as pigmented villonodular synovitis, which was comfirmed by the MRI examination and arthroscopy in knee.④ The rate of high effective biopsy in patients with high-grade synovitis (n=97) was 89%, which was significantly higher than that in patients with low-grade synovitis (n=176, 67%, x2=15.469, P<0.001).⑤ The rate of effective biopsy in swelling knee with tenderness was 89%, which was significantly higher than that in tendered knee without swelling (x2=5.458, P=0.019) or in knee without swelling or tenderness (x2=8.906, P=0.003).Conclusions: Qualified synovium obtained from Parker-Pearson needle biopsy could fulfill the need of clinical pathological examination and basic research.The degree of pathological synovitis and joint swelling are the major factors affecting the rate of effective biopsy.