An ultrasensitive dihydroxybenzene (DHB) quantitative detection method was developed based on the fluorescent graphene quantum dots (GQDs). In the presence of H 2 O 2 and horse radish peroxidase (HRP), DHB could be oxidized to the corresponding benzoquinone which could efficiently quench the fluorescence of GQDs. The fluorescence intensity ratio of GQDs (I/I 0 ) was proportional to the concentration of o-dihydroxybenzene (o-DHB), m-dihydroxybenzene (m-DHB) and p-dihydroxybenzene (p-DHB) in the concentration ranges of 0.5–250, 1–120, and 0.5–90nM, respectively. The detection limits are 2.0×10 −10 mol/L, 8.0×10 −10 mol/L and 3.0×10 −10 mol/L, which were much more sensitive than previous reports. In addition, the present method could be used for DHB sensing in rainwater and tap-water samples, and had a potential application for detecting various analytes which can be translated into benzoquinone in aqueous solution.