The research involves developing eco-friendly polymer composites by combining synthetic unsaturated polyester resin (UPR) with treated and untreated leather fibers (LF), cow hair fibers (CHF), and chicken feather fibers (CFF). By using these natural fibers instead of synthetic polymer, we aim to reduce the environmental impact while finding new purposes for waste materials from the poultry and tannery industries which would otherwise end up in garbage. The fibers were incorporated into the resin matrix at various weight percentages such as 2, 5, 7, 10, 12, and 15 % (w/w). Additionally, the properties of composites were improved by the addition of different types of inorganic nanoparticles, like CaCO3, Al2O3, and ZnO to the UPR matrix. These composites where inorganic materials were added as filler revealed better results than the neat composites. The composites showed the maximum overall mechanical properties in the bending modulus (BM), bending strength (BS), tensile modulus (TM), and tensile strength (TS) when 5 % of cow hair and chicken feather mixed fiber was used and ZnO was added as filler compared to the other composites. The highest values 4400.415, 68.91, 1788.74, and 34.95 N/mm2 of BM, BS, TM, and TS respectively, were found for the CFF + CHF + UPR + ZnO composite. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) supported mechanical rather than chemical connections between fiber and UPR. Ionizing gamma radiation-modified fiber exhibited superior tensile characteristics when 5 % of cow hair and chicken feather mixed fiber was used.