A high vascular patency was realized in the bulk or surface heparinized small-diameter in situ tissue-engineered vascular grafts (TEVGs) via a rabbit carotid artery replacement model in our previous studies. Those surface heparinized TEVGs could reduce the occurrence of aneurysms, but with a low level of the remodeled elastin, whereas those bulk heparinized TEVGs displayed a faster degradation and an increasing occurrence of aneurysms, but with a high level of the regenerated elastin. To combine the advantages of the bulk and surface graft heparinization to boost the remodeling of elastin and defer the occurrence of aneurysms, a coaxial electrospinning technique was used to fabricate a kind of small-diameter core/shell fibrous structural in situ TEVGs with a faster degradable poly(lactic-co-glycolic acid) (PLGA) as a core layer and a relatively lower degradable poly(epsilon-caprolactone) (PCL) as a shell layer followed by the surface heparinization. The in vitro mechanical performance and enzymatic degradation tests revealed the resulting PLGA@PCL-Hep in situ TEVGs possessing not only a faster degradation rate, but also the mechanical properties comparable to those of human saphenous veins. After implanted in the rat abdominal aorta for 12 months, the good endothelialization, low inflammation, and no calcification were evidenced. Furthermore, the neointima layer of regenerated new blood vessels was basically constructed with a well-organized arrangement of elastin and collagen proteins. The results showed the great potential of these in situ TEVGs to be used as a novel type of long-term small-diameter vascular grafts.