Twenty cases of the rheumatoid arthritis was carried out the histopathological observation from the affected synovial membrane at the knee joint by the Cops biopsy needle, at the Department of Orthopedic Surgery, Chosun University Hospital. The authors researched the difference to compare with the histological finding and its clinical features. The following results were obtained. 1. The average age was 36.9 years old and the sex ratio between the male and female was 1:2.7. 2. The erythrocyte sedimentation rate and protein amont in the synovial fluid was elevated than the normal value. 3. The most common clinical sign was the morning stiffness with multiple joint pain and moderate swelling, tenderess in the involved joint. 4. The test of rheumatoid factors revealed positive about 70% in the serum and 100% in the joint fluid. 5. The characteristic histological finding on the light microscopical examination was the hyperplasia of surface lining cells, deposition of the fibrin with the fibrinoid necrosis, and vascular hypertrophic changes of the blood vessel in all of those cases. 6. The histological finding had no difference to compare with the clinical course.