Microcarrier cell culture systems provide one of the most promising techniques for cell amplification due to their high surface area-to-volume ratio. In this study, biodegradable polycaprolactone (PCL) microspheres tethered with carboxylated poly(glycidyl methacrylate)-REDV conjugates were developed by a combination of surface-initiated atom transfer radical polymerization (ATRP) and azide-alkyne click chemistry as conducive microcarriers for rapid cell expansion of human umbilical vein endothelial cells (HUVECs). Azido-terminated poly(glycidyl methacrylate) (PGMA-N3) brushes were grafted onto the PCL microspheres by surface-initiated ATRP. Subsequent carboxylation of PGMA-N3 brushes was accomplished by azide-alkyne click reaction with hexynoic acid. REDV peptides were covalently conjugated to the pendent carboxyl groups on the side chain of carboxylated PGMA-COOH brushes via carbodiimide chemistry to enhance the cytocompatibility of the three-dimension (3D) PCL scaffolding system. Success in each functionalization step was ascertained by the measurement of attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and wet laser particle size analysis. In vitro cell-loading assay of HUVECs demonstrated a significant improvement of cell adhesion and proliferation on the REDV-immobilized PCL microsphere surfaces, and a confluent layer of HUVECs was formed after 7 days of incubation. The highly biocompatible and transportable nature of functionalized PCL microcarriers offers significant potential as a cell expansion platform.