Objective To investigate the mechanism of decorin inhibiting scar formation in a rat osteomyelitis model by investigating the expressions of tumor growth factor (TGF)-β1,phosphpo-Smad3 (p-Smad3) and collagen Ⅰ in skeletal muscle.Methods Sixty SPF rats were subjected to a muscular contusion injury with a self-improved blunt device.At postoperative 0,5,10,15,20 and 25 days,the rats were assigned to receive intra-muscular injection of 50 μl PBS (Group A,n =30) and 10 μg/ml decorin (Group B,n =30) respectively according to the random number table.Skeletal muscle samples from the rats were removed 7,14 and 28 days after the last iujection.Scar of the skeletal muscle was observed by HE staining.Expressions of TGF-β1,p-Smad3 and collagen Ⅰ were analysed by western blot.Results At days 14 and 28,HE staining showed tissue fibrosis in Group B was significantly reduced compared to Group A.At day 7,expression levels of TGF-β1,p-Smad3 and collagen Ⅰ in Group A were 0.152 ±0.031,0.439-±0.035 and 0.714 ±0.116 respectively compared to 0.145-±0.039,0.446 ±0.036 and 0.712 ±0.078 in Group B (P ＞ 0.05).At day 14,expression levels of TGF-β1,p-Smad3 and collagen Ⅰ in Group A were 0.263 ± 0.015,1.082-± 0.017 and 1.171 ± 0.138 compared with 0.136±0.004,0.155 ±0.040 and 0.217 ±0.025 in Group B (P ＜0.05).At day 28,expression levels of TGF-β1,p-Smad3 and collagen Ⅰ were 0.754 ± 0.042,1.197 ± 0.086 and 1.825 ± 0.044 in Group A compared with 0.307 ± 0.006,0.193 ± 0.028 and 0.256 ± 0.057 in Group B (P ＜ 0.05).Conclusion Local intra-muscular injection of decorin can reduce scar formation in a rat osteomyelitis model through inhibiting TGF-β-p-Smad3-collagen Ⅰ signaling pathway.