Polypyrrole (PPy)/poly(methyl methacrylate) (PMMA) core/shell nanospheres with diameters of several tens of nanometers have been synthesized by two-step microemulsion polymerization, and highly transparent conductive thin films have been fabricated using the nanospheres as a filler in a PMMA matrix. The PPy/PMMA core/shell nanoparticles and their composite films have been extensively characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared (FT-IR) and UV-vis spectroscopies, and electrical-conductivity measurements. The fabricated polymer films containing the PPy/PMMA core/shell nanofillers show a much better transparent conductive performance than that of uncoated PPy nanoparticles with similar dimensions or bulk PPy particles with diameters of several hundreds of nanometers. The PMMA shell promotes compatibility of the conductive fillers with the PMMA matrix and enhances dispersion of the PPy/PMMA core/shell nanofillers. In addition, the nanometer-thick PMMA shell has a lower glass-transition temperature (Tg), and can be effectively annealed to form a conductive-filler network with a high electrical conductivity at a relatively low filler content.