Nanostructures made of titanium dioxide and/or platinum nanoparticles supported on reduced graphene oxide (RGO) were synthesized by a simple and fast microwave-assisted route and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) and Raman spectroscopies. The composites consist of RGO sheets fully and homogeneously coated with a dense layer of 8 nm TiO2 and/or 2 nm Pt nanoparticles. Screen-printed flexible sensors based on Pt–TiO2/RGO composites are applied for the amperometric detection of hydrogen peroxide (H2O2). The electrochemical characteristics of Pt/RGO, TiO2/RGO and Pt–TiO2/RGO-modified screen printed electrodes are investigated and discussed. The developed sensor allows the detection of H2O2, with a linear response from 0 to 20 mM of H2O2 and a sensitivity of 40 μA mM−1 cm−2. The resulting device is also suitable for the analysis of this toxic compound in milk.