Phenolcamphor has been used for prevention of infection and for treatment of injury and suppurative inflammation of knee joint since the World War Ⅰ. Effects of Phenolcamphor in joint, especially regarding its corrosive action, were studied. Anatomical changes developing in joint were studied macroscopically and histologically by means of Hematoxylin-Eosin and PAS stain in two groups of rabbits in which 0.25 cc and 0.5 cc of Phenolcamphor were injected into knee joint, respectively. 1) Phenolcamphor properly prepared after original method neither produces necrosis of synovial membrane and articular cartilage nor has corrosive action. 2) Phenolcamphor must be carefully injected, for arthritis deformans would be caused by technical error, and its possibility is enhanced by presence of injury of articular cartilage. 3) Effects of Phenolcamphor continues so that persistent congestion is present in synovial membrane, and dilatation of small vessels, round cell infiltration and hyperplasia of connective tissue are histologically barely noticeable. A small amonnt of serous exudate accumulates, however, neither adhesion nor functional disturbances are produced.