A feasible processing of zwitterionic polymer-grafted anodic aluminum oxide (AAO) membranes by surface-initiated atom transfer radical polymerization (SI-ATRP) and the geometric effect on the polymer chain growth in the confined nanopores were investigated. A zwitterionic poly(3-(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate) (PMAPS) brush was produced on an AAO membrane via introduction of an initiator with a phosphonate group and subsequent SI-ATRP. The PMAPS-grafted AAO membranes were characterized by water droplet contact angle measurement, size exclusion chromatography (SEC), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and laser Raman micro-spectroscopy. The linear relationship between the grafting yield (Y) of the PMAPS brush and number-average molecular weight (Mn) of the unbound PMAPS indicates that there is no significant geometric effect on the chain growth under the spatial confinement inside the nanopores with diameters of ∼200 nm. The PMAPS brushes were diminished near the center section along the nanopores because the monomer supply was retarded. The capability of the PMAPS-grafted AAO membranes for inorganic nanoparticle immobilization was also demonstrated using gold nanoparticles (AuNPs) through ion-exchange and reduction processes.