The present study reports the synthesis of gold nanoparticles (AuNps) from gold precursor using palm oil mill effluent (POME) without adding external surfactant, capping agent or template. The biosynthesized AuNps were characterized by using UV-vis spectroscopy, transmission electron microscopy (TEM). X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). According to the image analysis performed on a representative TEM micrograph by counting 258 particles, the obtained AuNps are predominantly spherical with an average size of 18.75 +/- 5.96 nm. In addition, some triangular and hexagonal nanoparticles were also observed. The influence of various reaction parameters such as reaction pH, concentration of gold precursor and interaction time to the morphology and size of biosynthesized AuNps was investigated. This study shows the feasibility of using agro waste material for the biosynthesis of AuNps which is potentially more scalable and economic due to its lower cost. (C) 2012 Elsevier Ltd. All rights reserved.