In this paper we report the results of the synthesis and characterization of optimally doped La-1-xNaxMnO3 thin films grown on SrTiO3 (100), NdGaO3 (100), and NdGaO3 (110) for thicknesses ranging from 11 to 82 nm. The effect of substrate nature and orientation, film thickness, and annealing procedure was investigated to optimize their magnetoresistance (MR). We obtained very smooth films displaying MR values greater than 70%, near room temperature.