Purpose: To evaluate the histologic effect(LM and EM findings)of nonablative LASER and thermal energy on knee joint capsule of rabbit. Material and Methods: The nonablative LASER and thermal energy was applied to the rabits(average age 36 weeks, weight 5 ㎏). There were divided into 4 groups with 6 rabbits in each. The group I received 6 watts of LASER, group Ⅱ 12 watts of LASER, group Ⅲ 60° of thermal energy, and group Ⅳ 70° of thermal energy. The histologic study included H-E, Massons trichrome stain and electron microscopy at immediate, 3 weeks and 6 weeks after operation. Results: The histologic finding in immediate after operation was shown a fibrous degeneration of collagen on all groups and related to the energy level. The histologic finding after 3 weeks showed fibrosis and this fibrosis related the level of energy. Especially the group IV was shown flattening of capsule and deep fibrosis. The histologic finding after 6 weeks was shown marked recovery of collagen arrangement and capillary proliferation in group Ⅰ,Ⅱ and Ⅲ. But in the group Ⅳ not recovered. Conclusion: The nonablative LASER or thermal energy can cause degeneration, fibrosis and contracture of joint capsular collagen.