Nanotechnology is emerging as one of the most important and revolutionizing area in research field. Nanoparticles are produced by various methods like physical, chemical, mechanical and biological. Biological methods of reduction of metal ions using plants or microorganisms are often preferred because they are clean, nontoxic, safe, biocompatible and environmentally acceptable. In the present study, Aspergillus fumigatus was used for the intracellular synthesis of gold nanoparticles. Stable nanoparticles were produced when an aqueous solution of chloroauric acid (HAuCl4) was reduced by A. fumigatus biomass as the reducing agent. Production of nanoparticles was confirmed by the colour change from yellow to pinkish violet after ∼72 h of reaction. The produced nanoparticles were then characterized by Fourier transform infrared spectroscopy (FT–IR), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction spectroscopy (XRD). SEM images of sample revealed that the nanoparticles were spherical, irregularly shaped with indefinite morphology. Biosynthesized gold nanoparticles were in the range of 85.1–210 nm in size. The presence of gold nanoparticle was confirmed by EDS analysis. Crystalline nature and face-centred cubic structure of synthesized gold nanoparticle was confirmed by XRD pattern.