We report a simple and efficient extracellular biosynthesis of silver and gold nanoparticles (Ag and AuNPs) using anaerobic enriched mixed bacteria (AEMB) for the first time. Biosynthesized silver and gold nanoparticles were characterized by UV–vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results demonstrated that as-prepared nanoparticles are spherical in shape with the size of 5–65 nm in range. For gold nanoparticles, 2–7 particles were self-assembled into 1D chain-like structure. FTIR results evidenced interaction between the nanoparticle's surface and the reductive groups. Additionally, the dominant bacterial species in the enriched mixed culture have been identified via PCR-DGGE and DNA sequencing analysis. It was found that major bands belong to Klebsiella pneumoniae, Lactobacillus amylotrophicious and Salmonella enterica, which were responsible for the rapid reduction of silver and gold nanoparticles. This simple and green protocol could be used to prepare large-scale and economically viable synthesis of other metallic nanoparticles.