PtRu/C anode electrocatalysts modified by Sn were prepared for ethanol oxidation reaction (EOR). Their phase structures, surface species, surface compositions, and EOR activities were characterized by XRD, XPS, temperature-programmed reduction (TPR), and CV, respectively. It has been found that in the PtRu/SnxC and PtSn/C alloy catalysts, some Sn alloyed with Pt to form Pt-Sn phase existed as the metallic state, however, the excess Sn existed as the amorphous SnO or crystalline SnO2. Surface analyses and electrochemical measurements suggest that the surface Ru and amorphous SnO instead of the crystalline SnO2 are important species for the promotion of EOR. As a result, compared with PtSn/C, the I06 was enhanced about 200% for the PtRu/C electrocatalyst with 10 wt% of Sn modification.