Objective- Comprehensive functional, histomorphometrical and immunohistochemical assessment of sciatic nerve regeneration through an inside-out vein graft in rat. Design- Experimental in vivo study. Animals- Fifty- four healthy male White Albino rats. Procedures- The rats were divided into three experimental groups (n=18), randomly: Sham-operation (NC), Transected control (TC) and Inside-out vein graft (IOVG). In NC group after anesthesia the left sciatic nerve was exposed through a gluteal muscle incision and after careful homeostasis the muscle was sutured. In TC group the left sciatic nerve was exposed the same way, transected proximal to the tibio-peroneal bifurcation leaving a 10 mm gap. In IOVG group the left sciatic nerve was transected the same way and proximal and distal stumps were each inserted into an inside-out vein graft. Each group was further subdivided into three subgroups of six animals each and were studied 4, 8, 12 weeks after surgery. Results- Functional analysis showed significant improvement of nerve function in IOVG than in TC group (P < 0.05). Morphometric indices and immuohistochemistry indicated that there were significant differences (P < 0.05) between IOVG and TC groups 12 weeks after surgery. Conclusion and Clinical Relevance- Inside-out vein graft technique has offered the hope of providing a biological method for achieving the peripheral nerve regeneration in the least harmful way that is available, easily performed and affordable. It also averts the need for foreign materials that are likely to provoke a foreign body reaction.