In this study, lanthanum oxide (La2O3) nanoparticles or lanthana were synthesized by the planetary ball milling method and then used as a filler for the preparation of the polypropylene (PP) based nanocomposites by solution mixing method. The PP used in the study was derived from the discarded saline bottles. The structural and the surface morphology of the synthesized lanthanum oxide nanoparticles were characterized by XRD, SEM and FTIR. The thermogravimetric analysis (TGA) study revealed that the thermal stability of the nano lanthana composites increased with the addition of the lanthanum oxide nanoparticles. The mechanical properties, such as Young’s modulus and tensile strength, were also improved by the addition of the lanthanum oxide nanoparticles to the PP matrix. The composites also showed antibacterial activity against Escherichia coli bacteria. This approach not only mitigates medical plastic waste and environmental impact but also paves the way for versatile polymer nanocomposites with extensive industrial applications, especially in biomedical packaging.