We explored the feasibility of human umbilical vein (HUV) as a small-caliber vessel substitute. HUVs of 50 fetuses were collected on spontaneous miscarriage or labor with the pregnant women's permission. Gestational age ranged 24-42 weeks, and parturients were 20-30 years old. Each sample was sliced into 5 mum frozen transverse sections and stained with hematoxylin-eosin (HE), Weigert, aniline blue, and orange yellow G. The geometric morphological indexes and microstructural component were measured by a computer image analysis system. The media thickness was 0.186, 0.203, 0.237, 0.264, and 0.268 mm at 24-27, 28-32, 33-36, 37-40, and 41-42 weeks, respectively (F = 133.35, p < 0.01); diameters were 1.861, 1.962, 2.303, 2.464, and 2.465 mm (F = 37.35, p < 0.01), respectively. The media thickness and diameter of HUVs increased with gestational age. The elastin content of media increased at 24-40 weeks, but the collagen content and collagen/elastin (C/E) ratio decreased. Elastin content in the proximal segment was higher than in the distal segment [10.16, 6.36 Aa%, (Aa% is the unit of relative content, ie, the ratio of absolute areas to the total tested area of smooth muscle, collagen and elastin in the vascular wall) F = 5.77-12.3, p < 0.05], with the collagen to elastin (C/E) ratio increasing from the proximal to the distal segment (F = 7.63-13.4, p < 0.05). Our results suggest that the microstructural component of HUVs (2.0-3.0 mm caliber) at 37-40 weeks of gestation was similar to that of the small-caliber arteries and had moderate amounts of collagen and elastin and good elasticity, i.e., a good C/E ratio; therefore, HUV may be a substitute for small-caliber arteries (e.g., brachial, ulnar, radial, right coronary, anterior tibial, and posterior tibial). HUV is one of several graft materials that may be used when autogenous saphenous vein is absent or inadequate.