In this study, eugenol loaded m-PEG/PCL nanoparticles were used to make better the anti-bacterial properties of eugenol in an attempt to eliminate the resistant bacteria. m-PEG/PCL copolymer was prepared by ring-opening polymerization of ε-caprolactone monomer in the vicinity of dry m-PEG and tin (II) octoate catalyst. Polymeric nanoparticles were prepared by nanoprecipitation procedure. The particle size and zeta potential of mPEG/PCL/eugenol were specified to be 157.23 ± 3.81 nm and − 6.95 ± 0.19 mv, respectively. The polymeric nanoparticle structure was identified by AFM, FT-IR, and DSC techniques. To evaluate and compare the anti-bacterial efficiency of m-PEG/PCL/eugenol and free eugenol, a turbidity assay was used in association with gram-positive and gram-negative bacteria. Images of SEM were taken from bacteria before and after exposure to the mPEG/PCL/eugenol. Colony-forming unit per milliliter (CFU/ml) method was considered to follow the effect of mPEG/PCL/eugenol on bacteria growth rate in the original hospital wastewater. The results showed that m-PEG/PCL/eugenol nanoparticles at 40 µM concentration show the enormous antibacterial effect at 37°C. In original hospital wastewater, m-PEG/PCL/eugenol in the concentration of 0.125 µM at 25 ° C showed the greatest growth decrease of microbial total count.