Despite the good clinical efficacy of interferon-alpha (IFNα) to treat some types of cancer and viral infections, this biological drug is underused given its severe adverse effects and high dosing parenteral regimens. Aiming to achieve a breakthrough in therapy with IFNα, this work reports for the first time on the design and full characterization of a novel nanomedicine of IFNα-2b-loaded chitosan nanoparticles (IFN-CT NPs) for oral delivery. IFN-CT NPs produced by ionotropic gelation, encapsulating approximately 100% of the drug, showed a size of 36 ± 8 nm, zeta potential of +30 mV (dynamic light scattering), and spherical morphology (transmission electron microscopy). The antiviral activity of IFN-CT NPs in vitro was comparable to that of commercial IFNα. Remarkably, both treatments stimulated the expression of IFN response genes to a similar extent in both noninfected and infected cells with Human Lymphotropic-T Virus type 1. Finally, oral administration of IFN-CT NPs (0.3 MIU) to CF1 mice showed detectable levels of IFNα in plasma after 1 h, whereas no IFNα was detected with a commercial formulation. These results are encouraging and open a new avenue for the administration of this biological drug in a minimally invasive, safer, and more patient-compliant way.