This work presents the synthesis of platinum nanoparticles supported on S-layer protein/polymeric particle systems, obtained by combining proteins isolated from Lactobacillus kefiri and an aqueous dispersion of acrylic particles. FTIR spectra of the protein/polymer supports did not show changes in the Amide I band of the proteins, suggesting that proteins maintained their conformation after adsorption. The SAXS spectra and DLS results are consistent with the formation of a protein corona around the polymer particles. After combining the supports with the platinum complex and subsequently reducing the combination with hydrogen at mild conditions, we obtained colloidal nanocomposite materials. In these, platinum nanoparticles with diameters around 3 nm located on the surface of the protein/polymer supports were observed by TEM. The obtained nanosystems showed catalytic activity in the reduction of p-nitrophenol with NaBH4 at room temperature with conversions of 100% for reaction times of 50 to 70 min.