Abstract: Objective To investigate the law of TGFβ/Smad signal molecule expression in midpalatal suture remodeling after subjecting to tensional strain loading.Methods 36 Wistar male rats of 5 weeks old were divided into experimental group and control group (including negative controls and blank controls).The expansion appliances were placed into rats in experimental group,with opening loops with an initial force of 0.49 N applied to midpalatal suture.After expansion for periods of 1,4 and 7 days,IHC staining was used to investigate the expression of TGFβ/Smad signal molecules during midpalatal suture expansion at different time points.Results In rat midpalatal suture expansion,expression of TGFβ1,2,3,Smad2,3 and 4 was upregulated,especially in marginal periosteum cells， osteoblasts,secondary cartilage layer，pulp cavity and mesenchymal cells in sutura fiber layer and marginal bone.Expression of Smad7 was kept in a low level.Conclusions Mechanical tensil stress may regulate the expression pattern of TGFβ/Smad in suture cells to stimulate their proliferation,which leads to suture distraction osteogensis.