Substrate-selective flower-like Pd nanoparticles were prepared using a simple electrodeposition method. The flower-like Pd-graphene nanocomposites showed excellent electrochemical properties, as proven by electrochemical impedance and cyclic voltammetry. Developed to serve as a sensor for simultaneous determination of catechol (CT) and hydroquinone (HQ), the Pd-graphene nanocomposite-modified glassy carbon electrode (Pd-graphene/GCE) displayed good electrochemical catalytic activity toward CT and HQ, which was attributed to the flower-like composite structure, i.e. high electrical conductivity and larger surface area of Pd-graphene nanocomposites. Several kinetic parameters were calculated, including the electron transfer number (n), proton transfer number (m), charge transfer coefficient (c), and apparent heterogeneous electron transfer rate constant (ks). Under optimized conditions, the oxidation peak current was linear over a range from 0.075 to 5 mM. The detection limits were 1.25 9 10 -6 mol/L for HQ and 1.0 9 10 -6 mol/L for CT (S/N = 3). The proposed Pd-graphene/GCE was applied to the simultaneous determination of HQ and CT in Songshan Lake water samples.