Poly(butylene adipate‐co‐terephthalate) (PBAT) was mixed with copper nanoparticles (Cu‐NPs) in concentrations of 1%, 3%, and 5% with particle size between 100 nm and 200 nm by the melting method. A morphological, thermal, and structural characterization of the nanocomposites (NCs‐PBAT/Cu) was performed to analyze the effect of the Cu‐NPs on the polymer chains, as well as to explain the influence on their crystallinity, and its influence on the thermomechanical and antibacterial properties. The percentage of crystallinity (Xc) increased 6.7% to 9.5% with the amount of Cu‐NPs in the matrix. E‐modulus was slightly improved from 84.04 to 87.7 MPa, in the same way the degradation temperature (Td) of the PBTA was improved from 420.7°C to 427.2°C for 5% loading of Cu‐NPs. In contrast, ΔHm decreased from 12.50 to 6.96 J/g, indicating that there was no significant modification of the PBAT chain, mainly by heterogeneous nucleation in the presence of Cu‐NPs, which act as a heat barrier. No blue or red shifts we observed in the nanocomposites Fourier transform infrared (FTIR) spectra, indicating there is no effective interaction between PBAT and Cu‐NPs. The nanocomposites showed excellent antibacterial properties inhibiting 100% of the strains Enterococcus faecalis, Streptococcus mutans, and Staphylococcus aureus, at 2 hours of treatment. For more resistant strains such as Acinetobacter baumannii, the NCs‐PBAT/Cu did not show antibacterial activity at any time of treatment. POLYM. COMPOS., 40:1870–1882, 2019. © 2018 Society of Plastics Engineers