PURPOSE: To design bioadhesive Gantrez AN (poly[methyl vinyl ether-co-maleic anhydride], PVM/MA) nanoparticles (NP) coated with vitamin B(12) (Vit B(12)), and investigate their application in oral antigen delivery. METHODS: The association of Vit B(12) to Gantrez AN nanoparticles was performed by the direct attachment of reactive Vit B(12) to the surface of the nanoparticles (NPB), or linking to the copolymer chains in dimethylformamide prior to NP formation (NPB-DMF). Nanoparticles were characterized by measuring the size, zeta potential, Vit B(12) association efficacy, and stability of Vit B(12) on the surface of the nanoparticles. In vivo bioadhesion study was performed by the oral administration of fluorescently-labeled nanoparticle formulations to rats. Both systemic and mucosal immune responses were evaluated after oral and subcutaneous immunization with ovalbumin (OVA) containing Vit B(12)-coated nanoparticles. RESULTS: The Vit B(12) nanoparticles displayed homogenous size distribution with a mean diameter of about 200 nm and a negative surface charge. The association efficiency of Vit B(12) to NPB-DMF formulation was about two times higher than to the NPB, showing also a higher surface stability of Vit B(12). The bioadhesion study demonstrated that NPB-DMF had an important tropism to the distal portions of the gut, which was about two and 3.5 times higher than the tropism observed for NPB and control NP, respectively (p < 0.05). Oral administration of OVA-NPB-DMF induced also stronger and more balanced serum anti-OVA titers of IgG2a (Th1) and IgG1 (Th2) compared to control OVA-NP. In addition, oral immunization with OVA-NPB-DMF induced a higher mucosal IgA response than subcutaneous administration. CONCLUSIONS: These results indicate the benefits of bioadhesive Vit B(12)-coated nanoparticles in oral antigen delivery eliciting systemic and mucosal immune response.