The development of an eco-friendly and reliable process for the synthesis of gold nanomaterials using microorganisms is gaining importance in the field of nanotechnology. In the present study, gold nanoparticles have been synthesized by reduction of aqueous gold ions using the culture supernatant of Aspergillus niger NCIM 616. The synthesis of the gold nanoparticles was monitored by UV-visible spectroscopy. The particles thereby obtained were characterized by UV, Fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The stability of the synthesized gold nanoparticles was analyzed by zeta potential measurement. Treatment of the fungal supernatant with aqueous Au+ ions produced nanoparticles with an average particle size of 12.79 +/- 5.61 nm. Different characterization studies showed that the extracellular enzyme secreted by Aspergillus niger NCIM 616 might be responsible for both formation and capping of the metal nanoparticles.