The purpose of this study was to investigate the effects of different durations of static progressive stretching (SPS) on posttraumatic knee contracture in rats, including range of motion (ROM), gait analysis, myofibroblast proliferation, and collagen regulation.The posttraumatic knee contracture model was established, and male Wistar rats were randomly divided into the 20-minute SPS treatment, 30-minute SPS treatment, 40-minute SPS treatment, untreated, immobilization, and control groups. At weeks 0, 1, 2, and 4 of treatment intervention, joint ROM and gait were measured and compared. Knee joint samples stained with hematoxylin and eosin and Masson trichrome were used to observe alterations in pathological structures. Collagen density and cell numbers in the posterior joint capsule were used to assess joint capsule fibrosis and inflammation. Immunohistochemistry was used to detect type I collagen and α-smooth muscle actin expression.The S30 group improved the most; ROM, stance, mean intensity, print area, and stride length were 115 (SD = 5) degrees, 0.423 (SD = 0.074) seconds, 156.020 (SD = 7.952), 2.116 (SD = 0.078) cm2, and 11.758 (SD = 0.548) cm, respectively. The numbers of myofibroblasts, fibroblasts, and inflammatory cells decreased, and collagen proliferation was significantly suppressed in the S30 group compared with the other groups.S30 significantly improved posttraumatic knee contracture in rats, with reduced type I collagen and α-smooth muscle actin expression, decreased the numbers of myofibroblasts and inflammatory cells, suppressed fibrotic and inflammatory changes in the joint capsule, and increased joint mobility. This study provided basic evidence for an optimal standard-of-care treatment approach for posttraumatic knee joint contracture in rats, which may have significance for humans.© The Author(s) 2021. Published by Oxford University Press on behalf of the American Physical Therapy Association. All rights reserved. For permissions, please email: journals.permissions@oup.com.