The natural nanoparticles of CaCO3, from eggshell and CaCO3/Ag, were investigated as candidates for biocide nanoparticles in a blend of thermoplastic elastomer, styrene???ethylene/butadiene???styrene (SEBS), and polyolefin, high-meltstrength polypropylene (HMSPP). The nanoparticles with silver (Ag) were synthesized by metal precursor method, and before the application in the polymer matrix, the nanoparticles were analyzed on dynamic lighting scattering (DLS) and Raman spectroscopy. After DLS and Raman analyses, the nanoparticles were evaluated in biocide tests against P. aeruginosa and S. auerus. The aim of this investigation was the blending and the injection molding in dumbbell samples with the nanoparticles. The characterizations were carried out by differential scanning calorimetry (DSC), thermogravimetry analysis,mechanical tests, X-ray diffraction, Raman spectroscopy, scanning electronmicroscopy, and energy-dispersive scanning and biocide tests. Correlation between size and particle distribution on the polymerwas founded. However, samples at higher concentrations (>1 wt%) do not show biocide activity.