A novel reduced graphene oxide/Sb 2 O 5 hybrid nanomaterial was prepared by a one-pot reaction process. The nanomaterial was characterized by different spectroscopic, microscopic and electrochemical techniques, demonstrating that the graphene sheets were doped with a Sb 2 O 5 thin film. A glassy carbon electrode coated with the hybrid material was further employed as support for the covalent immobilization of laccase to develop an electrochemical biosensor for estriol. The enzyme biosensor showed high sensitivity (275 mA/M) and fast analytical response (4 s) for the hormone, with a limit of detection of 11 nM in the range of 25 nM to 1.03 mM. The biosensor showed high selectivity for the analytical detection of estriol.