Objective To investigate whether human p27kip1 gene transfection mediated by nanoparticles( NP) can express p27kip1 protein and inhibit the neointimal formation in rat vein grafting models. Method Autogenous vein graft model was established in 120 Wistar rats by transplanting internal branch of jugular vein to carotid artery. Rats were divided into three groups: (1) p27 group; p27kip1 gene mediated by NP were transfected into the veins before anastomosis; (2) control group; the veins were transfected by simple NP; (3) grafting group;the veins were grafted without transfection. The grafted veins were harvested at 3 d, 7 d, 14 d and 28 d respectively after the operation. The exogenous p27 kip1 protein expression in veins was determined by Western blot. Intimal hyperplasia (IH) and PCNA were observed by pathology and analyzed by computer digitizing system. The presence of apoptotic VSMC was demonstrated by TUNEL method. Result p27kip1 gene transfection mediated by NP complex increased protein expression of p27kip1 gene and there was a significant decrease in the intimal average thickness at 7 d, 14 d and 28 d in p27 group (P