The low-temperature behavior of the resistance of polycrystalline thin films of magnetoresistive manganites has been investigated for grain sizes in the nanometric scale. We have optimized the de-sputtering deposition and annealing procedures so as to meet the grain size requirements while keeping the basic features of the magnetic and electronic transport of the bulk material. A systematic upturn of the resistance at approximately 50 K is observed in all films (12-80 nm grain diameter). These results point to the existence of a Coulomb gap affecting the conduction of electrons at least in the smallest grain sizes explored. The evolution of this effect with the magnetic field is also investigated. (C) 2000 Elsevier Science S.A. All rights reserved.