We report a new, facile and one-step polyol route for the synthesis of Rh-on-Pd bimetallic nanodendrites that are composed of Pd cores with Rh branches. Ethylene glycol is used as a reducing agent while hexadecyltrimethylammonium bromide (CTAB) is used as a structure-directing agent. The as-synthesized nanodendrites are characterized by transmission electron microscopy, energy-dispersive X-ray spectrometry, X-ray diffraction and X-ray photoelectron spectroscopy. It is demonstrated that the morphology and number of Rh branches can be regulated by varying, respectively, the molar ratio of Pd to Rh precursors and the CTAB content. An intriguing finding is that CTAB not only directs the growth of Rh branches but also enables the formation of uniformly-shaped Pd cores. This effective one-step polyol synthesis can be ascribed to the different reduction kinetics between Pd and Rh ions resulting in the formation of Pd cores prior to the growth of the Rh branches. The electrocatalytic properties of the carbon supported Rh-on-Pd bimetallic nanodendrites as the catalyst for ethanol oxidation in alkaline media are investigated. Cyclic voltammetry results show that the Rh-on-Pd/C catalysts display a much higher CO₂ selectivity than a Pd/C catalyst. In particular, the ratio of the forward to backward peak current density (j_f/j_b) of the Rh-on-Pd (3 : 1)/C catalyst is 2.2, which is three times that of the Pd/C catalyst.