No　satisfactory　effects　have　been　obtained　with　the　use　of　synthetic　blood　vessels　(diameter　＜　6　mm)　as　substitutes　for　human　small　arteries　or　veins　for　the　purpose　of　clinical　vascular　reconstruction.　Therefore,　blood　vessels　of　human　origin,　for　example,　umbilical　cord　blood　vessels,　with　their　wide　availability,　still　should　be　considered.　However,　little　information　on　biomechanical　properties　of　human　umbilical　cord　blood　vessels　is　available.　The　objective　was　to　provide　a　theoretical　basis　for　the　clinical　application　of　umbilical　cord　veins　as　optional　material　for　small-caliber　grafts.　This　was　a　nonrandomized,　noncontrolled　in　vitro　study.　The　experiment　was　conducted　in　the　Laboratory　of　Medical　Biomechanics,　Yunyang　Medical　College.　Umbilical　cord　veins　of　20　normal　fetuses　of　spontaneous　labor　were　collected　by　the　Department　of　Obstetrics　and　Gynecology,　Taihe　Hospital　in　Shiyan　City,　Hubei　Province.　The　fetuses　aged　37-40　weeks,　and　the　parturients　were　20-30　years　old.　Umbilical　cord　veins　of　the　20　fetuses　were　used　and　the　placental　ends　were　treated　as　proximal　ends　while　the　fetal　ends　as　distal　ends.　The　fetal　ends　were　divided　into　three　segments:　proximal,　middle,　and　distal　segments.　The　relationship　between　pressure　of　umbilical　cord　veins　segments　and　the　diameters　was　measured　on　the　biomechanical　experiment　stand　for　soft　tissues,　and　then　the　elastic　modulus　was　calculated.　The　materials　were　transversely　extracted,　refrigerated,　and　sliced　up　before　HE　staining.　The　geometrical　morphology　indexes　were　measured　by　a　computer　image　analysis　system　(Leica-Q500IW).　The　main　outcome　measures　were:　incremental　elastic　modulus　(E-inc),　pressure-strain　elastic　modulus　(E-P),　volume　elastic　modulus　(E-v),　diameter,　and　wall　thickness　of　the　veins.　E-inc,　EP,　and　E,　of　umbilical　cord　veins　of　proximal,　middle,　and　distal　segments　increased　with　the　pressure　elevated.　The　three　kinds　of　elastic　modulus　of　proximal　segments　(E-inc:　26.98　+/-　3.21,　E-P:　16.58　+/-　2.12,　E-v:　8.31　+/-　2.35)　were　all　lower　than　those　of　distal　segments　(E-inc:　33.20　+/-　4.21,　E-P:　119.45　+/-　2.87,　E-v:　9.71　+/-　1.32)　(F　=　95.74-126.52,　p　＜　0.05),　and　a　tendency　to　increase　was　shown　from　proximal　segments　to　distal　segments.　Media　thickness　[(0.30　+/-　0.05)]　mm,　(0.24　+/-　0.03)　mm]　and　the　diameters　[(3.07　+/-　0.12)　mm,　(2.30　+/-　0.13)　mm]　decreased　gradually　from　proximal　to　distal　segments　(F　=　12.76,p　＜　0.01).　It　is　feasible　to　use　umbilical　cord　veins　as　substitutes　for　the　transplantation　of　small-caliber　arteries　in　terms　of　basic　biomechanical　properties.　On　vascular　grafting,　different　segments　of　umbilical　cord　veins　should　be　chosen　cautiously　so　that　the　biomechanical　characteristics　of　umbilical　cord　vein　grafts　could　be　in　accordance　with　those　of　host　to　increase　the　long-term　patency　rate　of　transplanted　blood　vessels.　(c)　2005　Wiley　Periodicals,　Inc.