Poly(methyl methacrylate)/single-walled carbon nanotube (PMMA/SWNT) composites were prepared via in situ polymerization induced either by heat, ultraviolet (UV) light, or ionizing (gamma) radiation. The composites dissolved in methylene chloride and then cast into films exhibited enhanced transparency as compared with the melt-blended composite material. UV/visible spectroscopy was used to quantitatively analyze the transparency of the composites. The dielectric constant (ε′) was measured via dielectric analysis (DEA) and correlated to the refractive-index values using Maxwell's relationship. The dielectric constant increased in the composite samples as compared with the neat PMMA samples prepared by the same methods. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) provided images of the polymer–nanotube composites and single-walled CNTs, respectively.