Biosynthesis of nano-gold particles (NGPs) is environmentally safer than chemical and physical procedures. This method requires no use of toxic solvents and synthesis of dangerous products and is environmentally safe. In this study, we report the biosynthesis of NGPs using Streptomyces mutabilis isolate B-2. Treating chloroauric acid solutions with this bacterium resulted in reduction of gold ions and formation of stable NGPs. TEM and SEM electro micrographs of NGPs were indicated size range of 2–12 nm with average of 7.5 nm produced intracellularly by the bacterium. SEM electro micrographs revealed morphology of spores and mycelia. The amplified PCR fragment of 16S rRNA gene was cloned and sequenced from both sides; it consisted of 825 nucleotides. According to NCBI GenBank, the bacterium had 97.6% homology with Streptomyces mutabilis strain 13676F. The GenBank accession number for partial 16S rRNA gene was recorded as JX162547. Optimized application of such findings may cause applications of Streptomycetes as bio-factories in eco-friendly production of NGPs to serve in demanding industries and related biomedical areas. Research in this area should also focus on the unlocking the full mechanism of NGPs biosynthesis by Streptomycetes.