Contracture is a very common complication in daily examination and a fibrotic change of a capsule is suggested to be a one of the main causes. Type I collagen is a major component of a synovial capsule and also has been implicated in tissue elasticity of other organs. We immobilized the knee joints of 66 rats in 150 degrees of flexion using a plastic plate and metal screws. Sham operated knee joints had holes drilled and screws inserted but none of them were plated. The expression patterns of type I collagen were characterized using in situ hybridization and immunohistochemistry. The in situ hybridization demonstrated that the mRNA of type I collagen decreased rapidly after immobilization. However, the immunoreactivity of the capsule was not changed in the immobilized and the control groups at any time points. Other processes might be considered to evaluate the contracture capsule.