Display omitted •Use of photochemical methods for producing nanocomposite.•Controlling the size of Prussian blue nanocubes in the nanocomposite.•Simultaneous electrochemical detection of ascorbic acid, dopamine, and uric acid. The practical application of Prussian blue (PB) for sensors is still limited due to its electrochemical properties that are dependent on factors such as the low stability at pH close to 7.0, the size and the shape of the material. In this sense, we report a green and facile strategy for one-pot synthesis of reduced graphene oxide/Prussian blue nanocomposites via photochemical method for sensing application. In the proposed method, graphene oxide was reduced simultaneously with the formation of PB nanocubes with controllable size, using sodium nitroprusside as precursor. The nanocomposite is more stable and sensible to electro-reduction of H2O2 when compared to PB at pH 7.4. The observed behavior is due to the ability of graphene to anchor the nanocubes and facilitate the electron transfer between the electrode and PB. Moreover, we also investigated the performance of the nanocomposite for simultaneous detection of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The sensor presented limits of detection of 34.7μmolL−1, 26.2μmolL−1, 8.0μmolL−1, for AA, DA, and UA, respectively.