In order to develop small-diameter vascular grafts， it is necessary to evaluate endothelialization， especially， in the center part at early stage. For implantation of vascular grafts of 1?cm in length to abdominal aortae of rat， endothelial cells can be formed easily by stretching anastomosis. We evaluated the endothelialization in the center part of vascular grafts by implanting vascular grafts using transgenic (TG) silk fibroin (SF) of 3?cm in length. Vascular grafts were prepared 1.5?mm in diameter and 1 and 3?cm in length using wild type (WT) SF and TG SF by braiding structure， respectively. The grafts were removed after 2?weeks or 3?months and evaluated pathologically. Endothelialization was not confirmed totally after 3?months of implantation. However， endothelialization in the center part of grafts was significantly higher in TG SF than in WT SF. No significant difference was found regarding tissue infiltration and internal diameter. The TG SF revealed migration of the endothelial cells into the center part of the vessels at the early stage. Also， tissue infiltration and remodeling is expected using SF. The 3?cm length vascular grafts can be evaluated as a new experimental system.