Surface modification of biodegradable vascular grafts is an important strategy to improve the in situ endothelialization of tissue engineered vascular grafts (TEVGs) and prevent major complications associated with current synthetic grafts. Important strategies for improving endothelialization include increasing endothelial cell mobilization and increased endothelial cell capture through biofunctionalization of TEVGs. The objective of this study was to assess two biofunctionalization strategies for improving endothelialization of biodegradable polyester vascular grafts. These techniques consisted of cross-linking heparin to graft surfaces to immobilize vascular endothelial growth factor (VEGF) or antibodies against CD34 (anti-CD34Ab). To this end, heparin, VEGF, and anti-CD34Ab attachment and quantification assays confirmed the efficacy of the modification strategy. Cell attachment and proliferation on these groups were compared to unmodified grafts in vitro and in vivo. To assess in vivo graft functionality, the grafts were implanted as inferior vena cava interpositional conduits in mice. Modified vascular grafts displayed increased endothelial cell attachment and activity in vivo, according to microscopy techniques, histological results, and eNOS expression. Inner lumen diameter of the modified grafts was also better maintained than controls. Overall, while both functionalized grafts outperformed the unmodified control, grafts modified with anti-CD34Ab appeared to yield the most improved results compared to VEGF-loaded grafts.