Extracellular matrices (ECM) derived from porcine tissue are associated with rapid and extensive repopulation with host cells when used as scaffolds for in vivo tissue repair. Cell adhesion to substrates used for tissue engineering has been studied extensively but the factors that mediate this phenomenon in ECM scaffolds following treatment with oxidants and sterilants have not been examined. Cell adhesion assays were used to examine human microvascular endothelial cell (HMEC) attachment to ECM graft materials harvested from small intestinal submucosa (SIS) and urinary bladder matrix (UBM) following decellularization and sterilization procedures designed to render the ECM safe for clinical use. HMECs were able to attach directly to these ECM scaffolds via several attachment proteins present within the ECM, including type I collagen, type IV collagen, and fibronectin. The ability of the SIS ECM and UBM ECM to support the growth and proliferation of HMEC was also examined. HMEC were able to grow to single-layer confluence on both surfaces of SIS and UBM sheets. The endothelial cells were also able to penetrate the SIS and UBM at later time points if they were seeded on the abluminal side of the ECM sheets. The ability of the processed ECM to support HMEC attachment and proliferation is similar to that reported for unprocessed ECM and may therefore play a role in the rapid remodeling response observed when these matrices are implanted in vivo as scaffolds for wound repair.