This study evaluated the endothelial function and mechanical properties of tissue-engineered vascular autografts (TEVAs) constructed with autologous mononuclear bone marrow cells (MN-BMCs) and a biodegradable scaffold using a canine inferior vena cava (IVC) model. MN-BMCs were obtained from a dog and seeded onto a biodegradable tubular scaffold consisting of polyglycolide fiber and poly(L-lactide-co-epsilon-caprolactone) sponge. This scaffold was implanted in the IVC of the same dog on the day of surgery. TEVAs were analyzed biochemically, biomechanically, and histologically after implantation. When TEVAs were explanted and stimulated with acetylcholine at 1 month, they produced nitrates and nitrites dose dependently. N(G)-nitro-L-arginine methylester significantly inhibited these reactions. With stimulation by acetylcholine, factor VIII-positive cells of TEVAs produced endothelial nitric oxide synthase proteins, and the ratio of endothelial nitric oxide synthase/s17 mRNA was similar among native IVC and TEVAs 1 and 3 months after implantation. TEVAs had biochemical properties and wall thickness similar to those of native IVC at 6 months after implantation, and tolerated venous pressure well without any problems such as calcification. The number of inflammatory cells in TEVAs and the ratio of CD4/s17 mRNA decreased significantly with time. These results indicate that TEVAs are a biocompatible material with functional endothelial cells and biomechanical properties and do not have unwanted side effects.