In situ growth of Pd-Pt alloy nanoflowers on host reduced graphene oxide (Pd-Pt ANFs/RGO) nanosheets by one-pot polyallylamine hydrochloride-assisted co-chemical reduction method, is developed. Compared with the common approaches to assembly of nanocatalysts in selected substrates based on pre-synthesized catalyst nanoparticles, the in situ fabrication is more facile, cost-effective and environment-friendly, allowing effective control of the location, distribution and uniformity of the supported Pd-Pt nanoflowers through the entire matrix. The detailed morphology; composition and structure of Pd-Pt ANFs/RGO nanocomposites are investigated by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), selected-area electron diffraction (SAED), energy dispersive spectrum (EDS), and nitrogen adsorption-desorption isotherms (SADI). TEM images show that Pd-Pt ANFs are directly grown on RGO with porous structure and good dispersion. Against commercial Pd/C catalyst, Pd-Pt ANFs/RGO nanocomposites show superior electrocatalytic activity, stability and satisfactory CO tolerance towards methanol oxidation reaction in basic electrolyte. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.