A novel drug carrier for brain delivery, poly(ethyleneglycol)-poly(ε-caprolactone) (PEG-PCL) polymersomes conjugated with mouse-anti-rat monoclonal antibody OX26 (OX26-PO), was developed and its brain delivery property was evaluated. The diblock copolymers of methoxy-PEG-PCL and Maleimide-PEG-PCL were synthesized and applied to prepare polymersomes (PO) which were verified by direct cryogenic temperature transmission electron micrograph (Cryo-TEM) imaging. The TEM examination and dynamic light scattering results showed that OX26-PO had a round and vesicle-like shape with a mean diameter around 100 nm. Coupling of OX26 with PO was confirmed by immuno-gold labeling of OX26 visualized under the TEM and X-ray photoelectron spectroscopy test. The surface OX26 densities were obtained from enzyme-linked immunosorbant assay. The result of brain delivery in rats proved that the increase of surface OX26 density of OX26-PO decreased blood AUC. The optimized OX26 number conjugated per polymersome was 34, which can acquire the greatest blood–brain barrier (BBB) permeability surface area product and percentage of injected dose per gram brain (%ID/g brain). Furthermore, NC-1900, as a model peptide, was encapsulated into OX2634-PO and improved the scopolamine-induced learning and memory impairments in a water maze task via i.v. administration. These results indicated that OX2634-PO is a promising carrier for peptide brain delivery.