The technological, thermal, and antimicrobial properties of biocomposite films produced from polylactic acid (PLA) and thermally treated wood flour with in situ generated nanosilver particles (AgNPs) using a bio-reduction method. The extracts of fresh leaves of the phenolic-rich Oriental sweetgum (Liquidambar orientalis) tree were used as the reducing agent for silver ions. Six different formulations of the mixed raw materials were extruded in the co-rotating twin screw extruder. The PLA bicomposite films at the 5 and 10 wt% loading levels of wood flour were produced by a hot press method from the following six formulations: (a) thermally treated wood + leaf extract + AgNO3, (b) untreated wood + leaf extract + AgNO3, (c) thermally treated wood + AgNO3, (d) untreated wood + AgNO3, (e) thermally treated wood, (f) untreated wood, and (g) neat PLA. All biocomposite films produced with the untreated/treated wood flour at 5 and 10 wt% loading levels of wood flour showed better tensile modulus than the neat PLA specimens. In general, the tensile strength of the biocomposites was negatively affected by the increased content of the wood flour. The spectra obtained from scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX) showed the silver nanoparticles in the wood particles. The results showed that the biocomposite films produced with PLA and wood flour modified using silver nitrate and leaf extract had the highest tensile modulus. It was observed that the leaf extract treatment had a positive effect on the tensile properties of the biocomposite films at 10 wt% content of wood flour. The remarkable antimicrobial results was obtained by the prepared biocomposites treated with gram positive and gram negative clinical pathogens at maximum zone of clearance 2.6 mm treated with E.coli bacteria.