Well-defined PtNi alloy nanoflowers supported on multi-walled carbon nanotubes (PtNi-H/MWCNTs) are successfully synthesized through a novel and potentially general one-pot reaction that exploits an in situ sacrificial template. The detailed morphology, composition, and structure of the PtNi alloy nanoflowers are investigated by transmission electron microscopy, energy-dispersive X-ray spectroscopy, nitrogen adsorption-desorption isotherms and X-ray diffraction. The results demonstrate that the PtNi-H/MWCNTs are highly porous. The electrocatalytic activity and stability of the PtNi-H/MWCNTs for the oxygen reduction reaction (ORR) are investigated by rotating disk electrode voltammetry in 0.1 mol L-1 HClO4 solution. The electrochemical tests indicated that PtNi-H/MWCNTs exhibited superior ORR activity along with satisfactory stability and methanol-tolerance under acidic conditions, which made them promising electrocatalysts. (C) 2014 Elsevier B.V. All rights reserved.