Promoting angiogenesis is one of the key targets of tissue engineering.However,angiogenesis of artificial nerve conduits in vivo is not fully understood.The aim of this study was to observe the angiogenesis of improved chitosan nerve conduits used to bridge 10 mm sciatic nerve defects in rats.At 1,3,6,9,12,and 14 days (n = 6 per group) after surgery,angiogenesis of the nerve conduits was observed and photographed with a stereomicroscope.At 14 days after surgery,the nerve conduits were frozen sliced,and stained with hematoxylin-eosin.New vessels grew into the nerve conduit from the two nerve ends by 6 days after surgery.A well-defined vascular network had formed by 14 days after surgery,and many blood vessels could be seen inside the nerve conduit wall.These results suggest that angiogenesis in improved chitosan nerve conduits used to bridge 10 mm sciatic nerve defects began at about 6 days after surgery and the vascular network formed at about 14 days after surgery.