2-Hydroxyethyl methacrylate and styrene block copolymer (HEMA-St) has been reported to show excellent blood compatibility in both in vivo and in vitro experiments. HEMA-St suppresses platelet adhesion and activation. The poor elastomeric properties of HEMA-St, however, have been an obstacle to application in small caliber vascular prostheses. We have developed a new amphiphilic block copolymer composed of HEMA and octyistyrene (HEMA-Octst) that improves the mechanical properties of HEMA-St. A small caliber vascular graft has now been fabricated using HEMA-Octst. The graft consists of a trilayered structure with Dacron composing the outer layer, polyurethane for the middle layer, and a HEMA-Octst coating for the inner layer. Three grafts were used in canine coronary artery bypass procedures to evaluate the grafts. Two of the grafts used in the coronary artery bypass were patent after 8～15 days. The HEMA-Octst coating did not show any surface cracks when examined using a scanning electron microscope, and the new grafts was sutured in place with 7-0 polypropylene sutures. HEMA-Octst has improved elastomeric properties and excellent blood compatibility. The material appears to be highly promising for applications in small caliber vascular prostheses that do not require an endothelial cell lining.