Autogenous donor nerve grafts facilitate nerve regeneration, but the source of material is limited, and harvest of these grafts results in donor site morbidity. Many types of artificial conduits have been studied as potential alternatives to short nerve grafts, however long nerve gaps were not successfully reconstructed due to lack of growth potential. Tissue engineering offers the potential to create replacement structures from autologous cells and biodegradable polymer conduits. Since they contain living cells, these structures have the potential to grow and induce regeneration. The objectives of this study are to create Schwann cells-seeded biodegradable nerve guide, and to assess in vivo nerve regeneration through the guides. A novel, biodegradable polymer conduit (2 mm in diameter, 0.5 mm in thickness, 25mm in length) was composed of a polycaprolactone-polylactic acid copolymer reinforced with woven polyglycolic acid. First, Schwann cells were isolated from Wistar rat sciatic nerve and expanded in vitro by eight weeks. Second, these cells were seeded into the polymer conduit via a low-pressure injection and centrifuge technique. Two weeks after seeding, Schwann cells culturing in a porous conduit wall were observed using electron microscope. Third, the Schwann cells-seeded conduits were used to bridge 20-mm defects in the Wistar rat sciatic nerve (n=8). Polymer conduits lacking Schwann cells (n=8) and silicone conduits (n=8) were implanted into another set of animals as controls. After 8 weeks, sciatic nerve including conduit was harvested and fixed by glutaraldehyde. At the mid portion of the conduit, cross sections were cut and stained with Toluidine blue to evaluate axonal contents. Electron microscopic study prior to grafting showed numerous number of Schwann cell culturing in a porous conduit wall with 3-dimensional manner. Histological assessment with light microscope at 8 weeks demonstrated excellent regeneration with well-myelinated fibers in the bridging tissue through the Schwann cells-seeded polymer conduits. In the untreated polymer conduits, four animals showed bridging tissue but nerve regeneration was poor. There was no regeneration through the silicone conduits. In morphological assessments, significant difference between Schwann cells-seeded and untreated conduits was detected in the total number of myelinated fibers (4125 � 581 vs 1220 � 268 respectively, p<0.01) and fiber density (fiber number / mm2 �F24554 �2654 vs 18902 � 1735 respectively, p<0.05). These findings suggest that tissue-engineered devices, composed of biodegradable polymer materials and adherent living Schwann cells can facilitate nerve regeneration in reconstruction for a long nerve gap.