Noble metal/polymer nanocomposites were prepared with homogeneous distribution of the metal nanoparticles in the polymer via in situ polymerization and subsequent thermal reduction. First, noble metal complexes having good compatibility with methyl methacrylate (MMA) were dissolved in MMA. The mixture was pre-polymerized by adding an initiator, and then transferred to a mold to complete the polymerization. The composites obtained were reduced in situ by post-heating at different temperatures, depending on the metal. X-ray CT and transmission electron microscopy were utilized to prove the uniform distribution of noble metal nanoparticles in the poly (methyl methacrylate) (PMMA). The noble metal nanoparticles have average diameters of similar to 3.0, 5.9, 12.7, and 24.1 nm for Pt, Pd, Cu, and Au, respectively. Thermogravimetric analysis shows that the weight of the Pd/PMMA nanocomposites increases with increasing initial molar concentration of metal complexes. UV/Visible transmission spectra also show plasmon absorptions characteristic of metals. The tensile strength of Pd/PMMA nanocomposites increased by 18.8% by adding Pd nanoparticles. These results suggest that uniform distribution of noble metal nanoparticles in PMMA can be achieved through in situ polymerization and thermal reduction.