Postoperative adhesions that restrict tendon gliding are a major cause of failure after tendon repair and grafting in Zone II. Several experimental reports have claimed that exogenously administered sodium hyaluronic acid (HA) helps to prevent the adhesion formation after digital flexor tendon repair. However, some investigators reported that HA had no effect on prevention of adhesion. Effectiveness of HA was determined by using an experimental chicken model. HA and physiologic saline solution was injected into the tendon sheath after partial cut of flexor digitorum profundus tendon. On light microscopy, cut ends revealed infiltration of neutrophils with scattered monocytes, 1ymphocytes and eosinophils at the second postoperative day in both control and HA treated goup. At the sixth and eighth postoperative day, the wounds were healed with granulation tissues and adhered to the tendon sheath in control group. Two weeks after operation both control and HA treated group were adhered to the tendon sheaths, but milder in HA treated group than that of control. After three weeks, adhesion to the tendon sheath was marked in both groups. Scanning electron microscopic findings were consistent with light microscopy. As results of above experiments, HA had a significant effect on prevention of adhesion until post-operative S days, and after 2 weeks no difference between HA and control group. No histological difference in process of tendon healing was observed between HA treated and control groups.