A novel graphene–Au nanoparticles (AuNPs) composite film modified glassy carbon electrode (GCE) was proposed for selective detection of dopamine (DA). The resulting electrode was characterized using transmission electron microscopy, cyclic voltammetry and differential pulse voltammetry. Compared to bare and graphene modified electrodes, this nanocomposite modified electrode not only significantly improved the electrochemical peak potential difference between DA and ascorbic acid (AA), but also noticeably enhanced the current response. The constructed DA sensor showed a wide linear range (5–1000 μM) and a low detection limit (1.86 μM). The graphene–AuNPs composite, which was obtained by assembling AuNPs onto the graphene surface, could provide a promising platform to develop excellent electrochemical sensors for detecting DA.