Abstract: Nanoparticles gene carriers, particularly nanoparticle gene carriers which exhibit increased rates of diffusion through cystic fibrosis (CF) mucus, as well as methods of making and using thereof, are described herein. The nanoparticle gene carriers are formed from a nucleic acid complexed to one or more biocompatible, polycationic polymers. The nanoparticle gene carriers also contain one or more mucus resistant polymers. In a particularly preferred embodiment, the nanoparticle gene carrier is a nanoparticle formed from one or more nucleic acids, PEI, and a mucus-resistant/diffusive graft copolymer composed of a PEI backbone functionalized by one or more PEG side chains. The nanoparticle gene carriers can efficiently diffuse through CF mucus, and can effectively serve as a vehicle to administer one or more nucleic acids to a patient suffering from CF.