In the treatment of peripheral neurological deficits, autologous nerve grafting is the first choice. The sural nerve, ante brachial cutaneous nerve, terminal branch of posterior interosseous nerve, and other choices are commonly used, however, loss of function and potential morbidity from creation of these donor sites are undesirable effects of their use. In recent years, synthetic nerve conduits and allogeneic nerve grafting materials have been introduced into clinical practice as alternatives to autologous nerve grafting [1-3]. The first attempt at nerve conduit was application for nerve regeneration using silicone tubes [4] Subsequent studies explored biodegradable materials with open internal structure as the conduit. More recently, filling the conduit with a regenerationconducive material such as collagen demonstrated improved nerve regeneration, however, the outcome remained inferior to autologous nerve grafting and allergenic nerve transplantation [5-7]. To promote nerve regeneration, biodegradable nerve conduits need to be carefully sutured to the donor nerves at the anastomotic site as the poor adaptation often allows fibroblasts invasion into the lumen of the conduit which hampers nerve regeneration. Unfortunately, no study has elucidated the influence of diameter discrepancy between the biodegradable nerve conduit and the donor nerve for better nerve regeneration. In this study, we introduced biodegradable nerve conduits of different diameter to examine how the diameter discrepancy influences nerve regeneration.