Sodium hyaluronate (HA) with a molecular weight of 202 × 104 (HA-202) was administered into the right knees of mature rabbits for the treatment of experimental osteoarthrosis induced by resection of the anterior cruciate ligament. At six and 12 weeks after the initiation of administration, the test group was compared with a group administered physiological saline solution to determine the effects on articular cartilage and synovial tissue. In both the six- and the 12-week period, cartilage degeneration proceeded with the lapse of time in both groups; however at 12 weeks, the efficacy of HA-202 in inhibiting degeneration was clearly observed at the lateral condyle of the femur and tibia where relatively marked degeneration was observed in the saline group. A comparison was also made among three groups administered HA-95 (sodium hyaluronate with a molecular weight of 95 × 104), HA-202, and saline, respectively, for 12 weeks. The saline group showed the greatest cartilage degeneration accompanied by complete disorganization of the cartilage layer and the disappearance of chondrocytes. The degeneration was less in the HA groups, and it was more significantly inhibited in the HA-202 group than in the HA-95 group.