Sorption of nanoparticles on mineral surfaces has been well recognized for its environmental implication. For certain gold ore deposits, sorption of gold nanoparticles (AuNPs) on pyrite may constitute a critical step in the metallogenesis process, yet it has not been adequately investigated. In this work, we synthesized negatively charged, positively charged AuNPs and pyrite respectively, and experimentally studied sorption of AuNPs on pyrite in an anaerobic environment. The effects of AuNPs charge characteristics, pH, hexadecyl trimethyl ammonium bromide (CTAB) concentration, and ionic strength were evaluated. For the negatively charged AuNPs, almost no sorption was observed owing to the electrostatic repulsion between the AuNPs and pyrite surface (with a measured isoelectric point of 2.0). In contrast, positively charged AuNPs could be significantly adsorbed on pyrite through electrostatic attraction, with the sorption extent decreasing with the increase of pH (2.2-9.1). However, the adsorption of CTAB from the solution was found to increase with the increase of pH. Furthermore, deliberately added CTAB seemed to inhibit the sorption of AuNPs. Our study not only demonstrates that the electrostatic interaction is the dominant mechanism in the sorption of AuNPs on pristine pyrite, but also reveals the important competitive relation between AuNPs and CTAB in the sorption process.