Using a rabbit model, we assessed the postoperative status and histopathologic findings of superior oblique tenotomy with silicone expander procedure. In the control group we marked and cut the superior oblique, and in the experimental group we inserted a silicone 240 retinal band 4 mm in length along the edges of incision. At the postoperative weeks 1,3,5 and 7, we randomly chose five rabbits and made a histopathologic examination after hematoxylin-eosin and Masson's trichrome stain. The distance between the incised edges was various in the control group, but constant in the experimental group. With time inflammation decreased and fibrosis of the superior oblique increased. Foreign body reaction occurred around the suture material in both groups., but not around the silicone expander. At 5 weeks atrophy of the superior oblique was observed in both groups.From the above results, we concluded that the superior oblique lengthening procedure using silicone expander is a useful surgical method for weakening the superior oblique muscle.