Osteoarthritic changes in experimental animals has been induced by several different methods. In order to study the changes of the articular cartilage induced by injuries of ligaments and/or meniscus of the knee joints, the author performed the experimental study that section of the medial collateral and anterior cruciate ligaments (group I) and section of the medial collateral and anterior cruciate ligaments combined with excision of the medial meniscus (group II) in twenty adult rabbit's knees caused instability. Histological changes of the articular cartilage were observed up to four months. The results were as follows: 1. The changes of the articular cartilage were gradually advanced depend on the time lapse after experimental procedures, in group I and ll. 2. The changes of the articular cartilage could be noticed from eighth week after experimental procedures in group I and from fourth week in group II, and more severe at sixteenth in group I and at twelfth week in group II. 3. The changes of the articular cartilage in group ll were appeared earlier and more severe than in group l. 4. The changes of the articular cartilage in the medial side of the knee joint were noticed more severe than in the lateral side.